Daf Yomi Kiddushin 29b - veLimadtem / ulmadtem -- Tifdeh / Tipadeh

I encountered the following recently in the Rif, daf 29b:

ללמדו תורה מנלן
דכתיב ולמדתם אותם את בניכם
והיכא דלא אגמריה אבוה מיחייב איהו למגמר נפשיה
דכתיב ולמדתם [ושמרתם]
ואיהי מנלן דלא מיחייבא לאגמורי
דכתיב ולמדתם ולמדתם כל שמצווה ללמוד מצווה ללמד וכל שאינו מצווה ללמוד אינו מצווה ללמד
ואיהי מנלן דלא מיפקדה
דכתיב ולמדתם ולמדתם כל שאחרים מצווין ללמדו מצווה ללמוד וכל שאין אחרים מצווים ללמדו אין מצווה ללמוד
ומנין שאין אחרים מצווין ללמדה
אמר קרא ולמדתם אותם את בניכם בניכם ולא בנותיכם:

To teach him Torah, from where for us?
For it is written {Devarim 11:19}:

יט וְלִמַּדְתֶּם אֹתָם אֶת-בְּנֵיכֶם, לְדַבֵּר בָּם, בְּשִׁבְתְּךָ בְּבֵיתֶךָ וּבְלֶכְתְּךָ בַדֶּרֶךְ, וּבְשָׁכְבְּךָ וּבְקוּמֶךָ.

19 And ye shall teach them your children, talking of them, when thou sittest in thy house, and when thou walkest by the way, and when thou liest down, and when thou risest up.

And where his father does not teach him, he is obligated to teach himself. For it is written {Devarim 5:1}:

א וַיִּקְרָא מֹשֶׁה, אֶל-כָּל-יִשְׂרָאֵל, וַיֹּאמֶר אֲלֵהֶם שְׁמַע יִשְׂרָאֵל אֶת-הַחֻקִּים וְאֶת-הַמִּשְׁפָּטִים, אֲשֶׁר אָנֹכִי דֹּבֵר בְּאָזְנֵיכֶם הַיּוֹם; וּלְמַדְתֶּם אֹתָם, וּשְׁמַרְתֶּם לַעֲשֹׂתָם.

1 And Moses called unto all Israel, and said unto them: Hear, O Israel, the statutes and the ordinances which I speak in your ears this day, that ye may learn them, and observe to do them.

And she, from where do we know that she is not required to teach? For it is written velimadtem {Devarim 11} ulmadtem. Anyone who is commanded to learn is commanded to teach, and anyone who is not commanded to learn is not commanded to teach.
And she, from where do we know that she is not so commanded? For it is written velimadtem ulmadtem. Anyone whom others are commanded to teach is commanded to learn, and anyone whom others are not commanded to teach is not commanded to learn.
And how do we know that others are not required to teach her?
Scriptures states:

יט וְלִמַּדְתֶּם אֹתָם אֶת-בְּנֵיכֶם, לְדַבֵּר בָּם, בְּשִׁבְתְּךָ בְּבֵיתֶךָ וּבְלֶכְתְּךָ בַדֶּרֶךְ, וּבְשָׁכְבְּךָ וּבְקוּמֶךָ.

19 And ye shall teach them your children, talking of them, when thou sittest in thy house, and when thou walkest by the way, and when thou liest down, and when thou risest up.

{most literally, sons}
Your sons and not your daughters.

The girsa in the Rif is slightly more explicit than the girsa in our gemaras. Specifically, when deducing the obligation for an individual to teach himself Torah if his father does not, Rif cites the pasuk as ולמדתם ושמרתם, while we lack the word ושמרתם. This is an important difference. We might have thought that the pasuk being cited was just ולמדתם, which would be the pasuk instructing to teach, in Devarim 11. And we would arrive at the obligation to learn via revocalization. Just as by pidyon, we had תפדה קרי ביה תיפדה. By adding ושמרתם, we know that the pasuk being cited is from Devarim 5.

Of course, working with our girsa of the gemara, it remains ambiguous. But Rashi says it is a kra achrina and points us to Devarim 5, and Artscroll follows his lead. It makes sense to say this, for two reasons: First off, it does not say קרי ביה, and secondly, why derive something from an al tikra when you have an explicit pasuk.

But then, when continuing, with דכתיב ולמדתם ולמדתם and so on, are we revocalizing, or are we channeling both Devarim 11 and Devarim 5. Artscroll goes with the revocalization theory. And like this, it matches nicely with what is done with תפדה. But again, why go this way, when in fact we have a pasuk which says this revocalization?

There is a systematic derivation of this, and pidyon, in Aramaic, using dichtiv rather than sheneemar, such that the style makes me think it is stammaitic. If so, I would venture that limmud Torah was first, since we have these psukim, and it works out nicely, while pidyon is patterned in similar way, making use of an al tikra to make them align nicely in this way.

But I can see questions. Why the need for an explicit pasuk, when we can learn from an al tikra, and so on.