Do the review ratings on Allmusic ever change?

Answer 1

Yes, they do. Some recent albums that were given 4.5 stars upon release were upgraded to 5 stars sometime in late 2008 or early 2009. I am not aware of any other ratings change or if there is a list of which albums have had their ratings bumped up.

Two examples of this would be "Is This It" by The Strokes and "Elephant" by The White Stripes. Both albums received 4.5 stars when they were first released but now have 5 star ratings. An easy way to verify this would be to look at the score recorded in Metacritic (though I should note that what Metacritic records is not always accurate to what the reviewer actually gave the album - personally, I can vouch for these two albums.)