GSX always had a variable number of carts, based on the payload when it originally came out, and this confused users a lot, and caused having to reply to the same question, over and over, "why I only see 1 cart", because they called GSX before setting the airplane payload, so we reverted to a simpler "always 3 cart" method, which put all support load about this issue to zero.
We might consider adding it again, only when Simbrief is used, so it won't be affected by the airplane payload changing when we don't expect.