1. Cowlings were formed by a combination of sheet metal being laid over (often concrete) forms and beaten with mallets (workers weren't called "tin-bashers" for nothing,) plus rolling machines, which made the chances of each being identical exceedingly remote. In "Spitfire the history" Jeffrey Quill complains about the (post-Packard Merlin 266 introduction) upper bulge, on one airframe, being so large it affected the handling.
2/. I often got a chance to chat with the Westland historian, and he once told me that Castle Bromwich (who built most Mk. IX Spitfires) airframes always had to retain their removable panels throughout repair, since they would never fit any other.
3/. When Stephen Grey was rebuilding a Spitfire, near here, Peter Cooke told him the cowlings they had wouldn't fit, and they laughed at him; a few days later, he got an apologetic phone-call, saying he was right, and asking why. "Because they're from an VIII, and you've got a IX." and everybody says that the VIII & IX are identical!!
4/. Try reading reports on how aircraft were inspected, and found ill-fitting, misshapen cowlings "persuaded" into place, often with a hammer, leaving drag-inducing gaps where they would cause the most trouble.
I hope, for those who have a genuine interest in research, and fact, rather than rhetoric, this information will show that wittering on about a half-millimetre, here or there on a model, has little or no relevance to the full-size, working subject.
Edgar