I wonder if the 4 radiators are the following:
Non GTI
8V GTI
16V GTI
G60/Rallye
And maybe by 91 they were getting rid of large stocks of everything ready for Mk3 production, and shoved any old thing on any car.
As an aside - can you post the part number that finally fits. I got my money on it starting 357 (i think).
Tin