Best I can tell, Accu-Guide is a design whereby small rectangular dimples are impressed into the feed lips of .45acp magazines.
These dimples don't appear on the .40s but some other small dimples do.
They seem to be on both AccuGuide and non-marked mags so apparently the design improvement was incorporated at the beginning of .40 production.
AS TTSH has pointed out, S&W applied for the patent in 1990 and were granted it in 1991.
1990 is when the .40s debuted so it's possible that S&W had bunches of unmarked mag bodies and bunches of marked mag bodies. (When these manufacturing companies produce or order components, they will order a very large number that is produced in a relatively short time, and then not re-order for years.)
And the same is probably true for the yellow and blue followers.
The blue follower was probably less an improvement than an easy way for S&W parts people to visually identify the marked mags.
But in the high demand days during the introduction of this pistol, by the time S&W was able to fill civilian orders, I don't doubt that they put whatever they had at the time in the box.

John