997/987 and 991/981 carbon folding buckets are identical the only difference being the later cars folding buckets were available with optional seat heating. Same number of cushions in both. The later cars were also available with 918 carbon fixed buckets that do not fold and I think they're a bit less supportive.

 

My 997 Carbon Folding Buckets no heating and notice the 2 seat cushions vs the 3 cushions in the original post. My car is factory spec NA car with buckets see VIN: WP0AC2A95BS783375 Also see this example here: https://rennlist.com/forums/market/1386795​​
cushion number doesn't make any difference to the use of the buckets. But it's a way to tell a difference between them. Note that 991(RoW) folding buckets do not have passenger occ sensor and require additional coding. Thats more a RoW vs NA thing.

 

Never seen a 997 with a three cushion seat but I have seen 991 with a 2 cushion Seat on the old style bucket. The new style 991 buckets, carbon fiber harness holes, have two cushions once again.

 

You're right never even noticed and I have 997 and 991 with folding buckets! 991 has seat heating option so you may need to update the base to 3 cushions for heating element to fit not sure.