The Rif's Girsa of the Mishna in Yevamot 120a

Here is a short one. The Mishna, as cited by the Rif on Yevamot 120a reads:

{Yevamot 120a}

אין מעידים אלא על פרצוץ פנים עם החוטם אע"פ שיש סימנים בגופו ובכליו.
ואין מעידין אלא עד שלשה ימים.
ואפילו ראוהו מגוייד או צלוב (על הצליב') וחיה אוכלת בו אין מעידין עד שתצא נפשו
רבי יהודה בן בבא אומר לא כל האדם ולא כל המקומות ולא כל העתות שוין

They {=a witness} may only testify {that the person died} if there is the full face with the nose, even if there are signs on his body and clothing {that it is him}.
{Different girsa. See the Mishna in the gemara. This follows the Mishna in the Yerushalmi.}
They only testify {if they saw the body} within three days {of death}.

And even if they saw his arteries cut, or crucified {on a cross}, or a wild animal eating his, they do not testify about him until his soul departs.
Rabbi Yehuda ben Bava says: Not every man, nor every place, nor every time is the same.

I wonder at the words in parentheses - על הצליבה. Where did they come from, if they are not original? It appears like a partial duplication of the words which remain -- או צלוב. The reason they are presumably marked out is that they seem unnecessary, for where will one be crucified if not on a cross? And furthermore, they do not appear in our Mishna in the gemara. Rather, our Mishna reads:

אין מעידין אלא על פרצוף פנים עם החוטם אע"פ שיש סימנין בגופו ובכליו
אין מעידין אלא עד שתצא נפשו ואפי' ראוהו מגוייד וצלוב והחיה אוכלת בו
אין מעידין אלא עד ג' ימים
ר' יהודה בן בבא אומר לא כל האדם ולא כל המקום ולא כל השעות שוין

But hold on one moment. There is a possibly more drastic change from the Mishna to the Rif's Mishna -- the placing of the phrase אין מעידין אלא עד שתצא נפשו, and the placing of the phrase ואין מעידין אלא עד שלשה ימים. In our Mishna in the gemara, the organization of the three phrases is:

1) Until his soul departs
2) even if they saw his arteries cut, or him crucified, or a wild animal eating him.
3) they do not testify about him except for having seen him the first three days after death.

This is a logical juxtaposition to Rabbi Yehuda ben Bava's statement about the nature of decomposition, but other structures are possible.

Meanwhile, the Rif's organization has:
3)
2)
1)

with (1) and (2) flipped.

However, before dismissing this order, I should note that often enough the Mishna in the Yerushalmi differs from the Mishna in the Bavli, and often the Rif's Mishna is the same as the Yerushalmi. This is one such case. The Mishna there {Yerushalmi Yevamot 82b} reads:

אין מעידין אלא על פרצוף פנים עם החוטם אף על פי שיש סימנין בגופו ובכליו אין מעידים אלא לאחר שלשה ימים.
אפילו מגוייד וצלוב על הצליב והחיה אוכלת בו אין מעידין אלא עד שתצא נפשו
ר' יודה בר בבא לא כל האדם ולא כל המקומות ולא כל השעות שוות

Which is essentially the same, and has the order of
3)
2)
1)

just as in the Rif's Mishna.

Furthermore, the Yerushalmi also has וצלוב על הצליב which is essentially the wording in the Rif's Mishna. Therefore, it has its basis and given only this evidence, I would say that we should preserve the phrase.

Update: Rashi in our gemara shows our gemara's order and text. Rashi does have על הצליבה but at least based on the punctuation we have, it is part of his commentary but not part of the dibbur hamatchil. I'm not sure how much stock to put into that division, though.

Rosh has the order as Rif:
3)
2)
1)
but does not have על הצליבה.