I think the Mini shells started off as Mk3 only, but now Heritage make Mk1 & 2 also? I’ve heard it said before about panel fit, but the panels were being made from original press tools, I think, then ‘hand built’. And as can be seen from a lot of ‘hand built’ cars, robots do a far better job! Who mentioned Morgan...
I remember that purists scorned the later Mini Mk1 or 2 front valance (that has the ends cut away), but in period if you were repairing a Mk1 you could only buy the later version after that model came out! Same with Mk1 E*s**rt (daren’t mention again...
) rear bumpers. Later cars had a cut out to allow more light for the number plate illumination, so immediately the early version was discontinued as a spare. Then of course when cars were being restored for concours, having the correct bumper mattered and they became quite valuable!