@Frosch: Why do the AuthorIDs need to be alphanumeric?
@Andy: It is easier to disable ABXX than AB10, AB20, AB30..., (mask against list) and it is kinda upwards compatible
(Edit: also it is much less likely that I produce a conflicting GRF, I just need to use "MG"0FXX as my next GRF, I do not need to check any GRF list.)
OzTrans solved this issue quite fair, he did not disable the issue causing GRF, he disables his own and let the player decide what to do.
I would not setup a database to claim "AuthorID"s, but link the
GRFID overview &
wiki from bananas so authors see if there are "similar" GRFIDs already around. Some coders work with masks, some with lists. But people with lists should respect already existing ranges and not use one from it just because their GRFs do not care about masks.
btw. I was sure back then that "MG" was free.

(Edit: confirmed, it was my last grf was around 2010 (! really that long ago?

, Yoshi started coding 2011)