That is almost certain, though it should be noted that it’s not always the case. For instance in the mid 70s exchanged the few “GS Birotor” it had sold for CXs

That is almost certain, though it should be noted that it’s not always the case. For instance in the mid 70s exchanged the few “GS Birotor” it had sold for CXs, which was higher in the range. The deal was very much in Citroen’s favour, but not to the client’s loss: the birotor was effectively pretty crummy (outside of being a collector model, which is how a few survived), and it was launched just as the oil crisis started powered by a gas-guzzling (and unreliable) rotary engine, as well as being almost double the price of a standard GS. As a result it sold extremely poorly (847 units were produced) and was quickly pulled. Citroen tried to buy / exchange them back (and did get most of them) so it didn’t need to support the car and keep spare parts through its network.