Magic number?

Early this morning I was thinking about alphabet songs and was struck by the thought that it was another manifestation of the rule of the magic seven, a rule which I notice from time to time, as can be seen at reference 1.

I very rapidly convinced myself that the rhyme I learned at infant school went with three groups of seven, followed by a terminal 5. That is to say (7, 7, 7, 5) or 'A, B, C, D, E, F, G', 'H, I, J, K, L, M, N', 'O, P, Q, R, S, T, U' and 'V, W, X, Y, Z'. With the three groups of seven being sung evenly, but with a bit of variation with the closing group of five to make it fit the tune properly.

Having now checked, I find lots of alphabet songs offered by google, with the one that seems most like my memory at reference 2 (illustrated). But rather than (7, 7, 7, 5), it goes (7, 9, 6, 4), with only the first line being sung evenly.

The version offered by BH, a former infant teacher, went (7, 9, 7, 3), with her 9 being scanned in the same way as the US version, with a quick 5 at the end, which was not how I remembered it at all.

So what is going on? Has the song changed since I was little? Do they do it wrong in the US? Were there lots of local variations before radios and google got in on the act? Or have I decided what I want to remember before I get around to the remembering, with the magic number not actually being as potent as I would have it?

Reference 1: http://psmv2.blogspot.co.uk/search?q=magic+seven.

Reference 2: http://supersimplelearning.com/songs/original-series/one/the-alphabet-song-sing-it/.