Merlin saw much less major iteration, but with that it's worth considering that there is a lot more experience with Kerolox engine design out there (plus a much

Merlin saw much less major iteration, but with that it's worth considering that there is a lot more experience with Kerolox engine design out there (plus a much simpler combustion cycle). Plus it was based on a NASA reference design. I do recall from Eric Berger's Liftoff book, they struggled with the nozzle design though. Very early Merlin had an ablative nozzle. I suppose the better way to put it might be that Merlin's iteration was more in getting the production sorted out, whereas Raptor is iterating everything based on lessons from Merlin and previous Raptor iterations.