Have had issues with check engine light coming.

Have had issues with check engine light coming on and engine power reduced kicking in recently. Brought it to dealer and they say it is a known issue with the throttle body that GM has acknowledged and the $600+ cost would be covered. I just had to authorize the $55 cost for the tech to inspect and confirm. Well. After inspection & issue confirmed, I was told my VIN# was NOT on GM's list to cover this problem! Say what? Anyone know how GM can nit pick certain vehicles to fix at no charge and yet others, with the exact same problem get to pay? Anyone know how to obtain the list of VIN#'s that are covered for issues & how those are determined? Was almost funny how the service tech was as surprised as I was to learn that of the "dozens of these they have fixed in the last month alone" that I am the first that gets to pay for it!