Yep, the flare rack was deleted from the seat. The Mk.I had a metal seat, and when the composite seat was introduced, the rack was deleted.
That said, it could still be present on some Mk.II and early Mk.V airframes, using the metal seat, although fairly rare by then. Note that a metal seat was re-introduced from the Mk.IX onwards, I think from mid production blocks, as there had been cases of the composite seat collapsing under high "g" with the more powerful later Mark Spits.
However, it was still possible to see the composite seat on later Marks.
Some restored Spits include the rack, which is probably why some kit manufacturers persist in reproducing it.