Very daft question. Are there different 'fits' of wintec saddles? Or are 17" GP's all the same with the adjustment coming from the gullet plate for high/low withers etc?
There are different models that might be slightly differently, and the Wintec Wide is a completely different shape to the other GP's.
However, they are saddles, like any other, so used examples may have changed shape over time or as a result of a roll / fall. Also, like any other saddle, they either fit your horse, or they don't, and as you say, the adjustability is only at the gullet and relatively limited.
In the past I have also modified a gullet insert to suit my pony. I would never sell it on, and the marks left by the vice are pretty evident, but there nothing stopping other people doing the same.
That would of course also invalidate any warranty. They do indeed vary a lot in their fit for both horse and rider. Do have a read here before purchase: