Chukat #1: For the border of Ammon was strong?

In a confusing statement towards the end of parshat Chukat, we read {Bemidbar 21:24}:

כג וְלֹא-נָתַן סִיחֹן אֶת-יִשְׂרָאֵל, עֲבֹר בִּגְבֻלוֹ, וַיֶּאֱסֹף סִיחֹן אֶת-כָּל-עַמּוֹ וַיֵּצֵא לִקְרַאת יִשְׂרָאֵל הַמִּדְבָּרָה, וַיָּבֹא יָהְצָה; וַיִּלָּחֶם, בְּיִשְׂרָאֵל.	23 And Sihon would not suffer Israel to pass through his border; but Sihon gathered all his people together, and went out against Israel into the wilderness, and came to Jahaz; and he fought against Israel.
כד וַיַּכֵּהוּ יִשְׂרָאֵל, לְפִי-חָרֶב; וַיִּירַשׁ אֶת-אַרְצוֹ מֵאַרְנֹן, עַד-יַבֹּק עַד-בְּנֵי עַמּוֹן--כִּי עַז, גְּבוּל בְּנֵי עַמּוֹן.	24 And Israel smote him with the edge of the sword, and possessed his land from the Arnon unto the Jabbok, even unto the children of Ammon; for the border of the children of Ammon was strong.

This seems to imply that the Israelites would have conquered further, into the territory of the children of Ammon, but for the fact that their border was strong, such that they could attack no further.

This would seem to contradict Dvarim 2:17-19:

יז וַיְדַבֵּר ה, אֵלַי לֵאמֹר.	17 The LORD spoke unto me saying:
יח אַתָּה עֹבֵר הַיּוֹם אֶת-גְּבוּל מוֹאָב, אֶת-עָר.	18 'Thou art this day to pass over the border of Moab, even Ar;
יט וְקָרַבְתָּ, מוּל בְּנֵי עַמּוֹן--אַל-תְּצֻרֵם, וְאַל-תִּתְגָּר בָּם: כִּי לֹא-אֶתֵּן מֵאֶרֶץ בְּנֵי-עַמּוֹן לְךָ, יְרֻשָּׁה--כִּי לִבְנֵי-לוֹט, נְתַתִּיהָ יְרֻשָּׁה.	19 and when thou comest nigh over against the children of Ammon, harass them not, nor contend with them; for I will not give thee of the land of the children of Ammon for a possession; because I have given it unto the children of Lot for a possession.--

That is, in Dvarim they do not invade the land of Ammon because of Divine decree, while in Bemidbar they do not invade because the border is strong!

Rashi gives an explanation of the pasuk in Bemidbar on the basis of the pasuk in Dvarim. The reason the border was strong was not the physical strength of the people, or their fortifications, or the geography, but the Divine decree of Devarim 2:19.

(I would read, then: for the border of Ammon was firm.)

There is another possible resolution, however, and that is that the word in pasuk 24 is not עז, strong, but rather יעזר, the city of Yaazer, which is perhaps situated about 10 to 15 miles north of Cheshbon, the city of Sichon, and thus on the Emorite/Ammonite border. Thus, the city is on the border of the sons of Ammon, but belonging to the Emorites, and thus they attack there but no further.

This variant text is found in LXX, that is the Septuagint:

In Greek:
21:24 και επαταξεν αυτον ισραηλ φονω μαχαιρης και κατεκυριευσαν της γης αυτου απο αρνων εως ιαβοκ εως υιων αμμαν οτι ιαζηρ ορια υιων αμμων εστιν.

In English:
24 And Israel smote him with the slaughter of the sword, and they became possessors of his land, from Arnon to Jaboc, as far as the children of Amman, for Jazer is the borders of the children of Amman.

We see later on in the same chapter that they attack Yaazer. Bemidbar 21:31:

לא וַיֵּשֶׁב, יִשְׂרָאֵל, בְּאֶרֶץ, הָאֱמֹרִי.	31 Thus Israel dwelt in the land of the Amorites.
לב וַיִּשְׁלַח מֹשֶׁה לְרַגֵּל אֶת-יַעְזֵר, וַיִּלְכְּדוּ בְּנֹתֶיהָ; ויירש (וַיּוֹרֶשׁ), אֶת-הָאֱמֹרִי אֲשֶׁר-שָׁם.	32 And Moses sent to spy out Jazer, and they took the towns thereof, and drove out the Amorites that were there.
לג וַיִּפְנוּ, וַיַּעֲלוּ, דֶּרֶךְ, הַבָּשָׁן; וַיֵּצֵא עוֹג מֶלֶךְ-הַבָּשָׁן לִקְרָאתָם הוּא וְכָל-עַמּוֹ, לַמִּלְחָמָה--אֶדְרֶעִי.	33 And they turned and went up by the way of Bashan; and Og the king of Bashan went out against them, he and all his people, to battle at Edrei.

Or in Greek:

21:32 και απεστειλεν μωυσης κατασκεψασθαι την ιαζηρ και κατελαβοντο αυτην και τας κωμας αυτης και εξεβαλον τον αμορραιον τον κατοικουντα εκει

This would resolve the Dvarim/Bemidbar contradiction, which makes the Yaazer option somewhat suspicious under lectio difficilior (in that it is a reason for the change from Az --> Yaazer). Note also the slight possibility that the adjoining letters in the surroinding Greek words: οτι ιαζηρ ορια. In Hebrew, there is the י of the word כי and the ג of גבול perhaps might be mistakes for a ר, depending on the specific pronunciation of each.

If the word was indeed originally יעזר, the yud, at least, could have been dropped, because it duplicated the י of כי in the preceding word, under the theory of Shadal, mentioned in this post, in which the following is cited:

He says that the ancient scribal practice was to leave out one letter when the same letter begins the next word. (He speculates that perhaps instead of this letter a certain sign was used to indicate that one letter stands for two.)

Update: There is an interesting parallel pasuk in the halftara, in the story of Yiftach, in Shofetim 11:14-18, Yiftach is answering the claim of the king of Ammon that the Israelites took away his land, when they came out of Egypt. Yiftach counters that the land they took was that of the Emori, and they did not intrude or take away from the land of either Moav or the children of Ammon.

יד וַיּוֹסֶף עוֹד, יִפְתָּח; וַיִּשְׁלַח, מַלְאָכִים, אֶל-מֶלֶךְ, בְּנֵי עַמּוֹן.	14 And Jephthah sent messengers again unto the king of the children of Ammon;
טו וַיֹּאמֶר לוֹ, כֹּה אָמַר יִפְתָּח: לֹא-לָקַח יִשְׂרָאֵל אֶת-אֶרֶץ מוֹאָב, וְאֶת-אֶרֶץ בְּנֵי עַמּוֹן.	15 and he said unto him: 'Thus saith Jephthah: Israel took not away the land of Moab, nor the land of the children of Ammon.
טז כִּי, בַּעֲלוֹתָם מִמִּצְרָיִם; וַיֵּלֶךְ יִשְׂרָאֵל בַּמִּדְבָּר עַד-יַם-סוּף, וַיָּבֹא קָדֵשָׁה.	16 But when they came up from Egypt, and Israel walked through the wilderness unto the Red Sea, and came to Kadesh;
יז וַיִּשְׁלַח יִשְׂרָאֵל מַלְאָכִים אֶל-מֶלֶךְ אֱדוֹם לֵאמֹר אֶעְבְּרָה-נָּא בְאַרְצֶךָ, וְלֹא שָׁמַע מֶלֶךְ אֱדוֹם, וְגַם אֶל-מֶלֶךְ מוֹאָב שָׁלַח, וְלֹא אָבָה; וַיֵּשֶׁב יִשְׂרָאֵל, בְּקָדֵשׁ.	17 then Israel sent messengers unto the king of Edom, saying: Let me, I pray thee, pass through thy land; but the king of Edom hearkened not. And in like manner he sent unto the king of Moab; but he would not; and Israel abode in Kadesh.
יח וַיֵּלֶךְ בַּמִּדְבָּר, וַיָּסָב אֶת-אֶרֶץ אֱדוֹם וְאֶת-אֶרֶץ מוֹאָב, וַיָּבֹא מִמִּזְרַח-שֶׁמֶשׁ לְאֶרֶץ מוֹאָב, וַיַּחֲנוּן בְּעֵבֶר אַרְנוֹן; וְלֹא-בָאוּ בִּגְבוּל מוֹאָב, כִּי אַרְנוֹן גְּבוּל מוֹאָב.	18 Then he walked through the wilderness, and compassed the land of Edom, and the land of Moab, and came by the east side of the land of Moab, and they pitched on the other side of the Arnon; but they came not within the border of Moab, for the Arnon was the border of Moab.

Compare this with Bemidbar 21:23-24, as cited above:

כג וְלֹא-נָתַן סִיחֹן אֶת-יִשְׂרָאֵל, עֲבֹר בִּגְבֻלוֹ, וַיֶּאֱסֹף סִיחֹן אֶת-כָּל-עַמּוֹ וַיֵּצֵא לִקְרַאת יִשְׂרָאֵל הַמִּדְבָּרָה, וַיָּבֹא יָהְצָה; וַיִּלָּחֶם, בְּיִשְׂרָאֵל.	23 And Sihon would not suffer Israel to pass through his border; but Sihon gathered all his people together, and went out against Israel into the wilderness, and came to Jahaz; and he fought against Israel.
כד וַיַּכֵּהוּ יִשְׂרָאֵל, לְפִי-חָרֶב; וַיִּירַשׁ אֶת-אַרְצוֹ מֵאַרְנֹן, עַד-יַבֹּק עַד-בְּנֵי עַמּוֹן--כִּי עַז, גְּבוּל בְּנֵי עַמּוֹן.	24 And Israel smote him with the edge of the sword, and possessed his land from the Arnon unto the Jabbok, even unto the children of Ammon; for the border of the children of Ammon was strong.

There is a marked parallelism here between the two verses. The one in Shofetim is stressing how they did not intrude past Moab's border, namely Arnon. The one in Bemidbar also stresses how they did not intrude past the children of Ammon's border, namely the Yabbok river. Thus, they only conquered current Emorite territory.

Indeed, the continuation in Bemidbar speaks about how Sichon king of the Emorites had previously captured Cheshbon from Moab, which makes it fair game. Indeed, the general trend (in Bemidbar and in Shofetim) seems to be the respecting of the borders of Ammon and Moav, in consonance with Hashem's decree, as spelled out in Devarim.

We would then expect this to be a reference to the border town, with the word "Ki" functioning as the reason they did not intrude farther . After all, just as Arnon was the border of Moav, Yabbok (or Yaazer) was the border of Ammon. Perhaps we can say that עז was a place name? :) Or perhaps this is a reference to the firmness of the border, because of the Divine decree.

Update: See here:

remained firm
(Targum). This was because God told the Israelites not to attack Ammon (Deuteronomy 2:19; Sefer HaYashar; Lekach Tov; Bachya). Others see Az here as a proper noun, which the Septuagint renders as Y'azer, see Numbers 21:32. The Torah is thus saying, 'Az was the border of Ammon.' Other sources apparently identify Az with Ar (Numbers 21:15, Lekach Tov ad loc.).