After collecting and checking out informations, here what can help narrow them down

GT : there is a colored red or blue stripe inside the molding . It was standard on the 1987 and 1988 models but became an option for 1989+ ones

Canadian ones are called Cobra GT up to 1992 , 1993 ones are simply GT

There is also a black one found on some cars in the database , i still need to find when it starts ( i think 1989 when the stripe became an option but it still only a theory for now )

LX : The stripe mentionned above was in the option list for the whole run but is smaller
1992-1993 have body colored moldings opposed to black for 1987-1991

both : mirror change on the convertible somewhere during the 1988 MY , coupe/hatch ones remain unchanged
T-top were available only for 1987-1988 , 1989+ couldn't get that option anymore
1989 ones have a Mustang badge on the dashboard for the 25th anniversary
1990 got driver side airbag , canadian ones got DRLs
1991 GT and LX 5.0 got the Pony wheels

will post pics later, on my mom's laptop , running out of gas and for a weird unknown reason its the only one that allows me to create a new topic ( my sister's and my half-laptop can't )