To be fair, 3x4 is a format that's not exactly in high demand. They do get 4x5 and 8x10 right (except maybe for the notches).
And the OP is communicating with an ebay seller - not with Shanghai.
I have some Catlabs 80 (rumored to be Shanghai GP3) in 8x10 that is (only sometimes) slightly large in the 10in dimension. Fortunately, the only issue it causes is the end by the flap doesnt settle inside the groove. I might cause slight film plane issues at the far end, but I've never seen it cause a problem. Nonetheless, the size issue has scared me off from buying any more Catlabs/Shanghai film.
To be fair, 3x4 is a format that's not exactly in high demand. They do get 4x5 and 8x10 right (except maybe for the notches).
And the OP is communicating with an ebay seller - not with Shanghai.
I received a fresh Shanghai GP3 3.25x4.25 50 sheet pack today (bought from eBay seller mytongguy), and they load without any problem to original Graflex double-side film holders. This pack shows batch number 10, so I guess the factory might have improved since. I'm not associated with the manufacturer nor eBay seller, just sharing the information for other 3x4 photographers.
I received a fresh Shanghai GP3 3.25x4.25 50 sheet pack today (bought from eBay seller mytongguy), and they load without any problem to original Graflex double-side film holders. This pack shows batch number 10, so I guess the factory might have improved since. I'm not associated with the manufacturer nor eBay seller, just sharing the information for other 3x4 photographers.
The Shanghai GP3 100 film from factory batch 4 has the following dimensions: 82 x 108mm (or 3 3/16 x 4 1/4).
It barely works with Mod54, but there is risk of popping out if the agitation is less than gentle. On the other hand, 9x12 film works totally fine with Mod54.
I probably under-exposed and under-developed the film ( I was using Clayton's F76+ 1+9, 7 min at 68F), so I'm having some strange mottling issues with image. I will do a bit more test before jumping into conclusions.