The inner fender liners are indeed a smaller size on the earlier models, BUT they will work fine in the later models. I installed a liner from an 88 or 89 in my 93, and it was noticeably a different size, but it fits with no problem, as it is very close to the other one. This information was also verified by the owner of Mustang Central, a mustang specialty shop where I bought the liner.
------------------
1993 GT/AOD
'93 Mustang GT