I just spent a little time wandering through lens formula schematics. Interestingly, the
Canon FL 55mm 1.2 and the
Topcon (pre Cosina) 58mm 1.4 have the same 7 element 5 group scheme with very similar element construction. The
Voigtlander remake is very close but is a 7 element six group design. This would explain, perhaps, why people were getting different results from the Topcon vs. the VL. Between the FL and the Topcon then it comes down to small details like construction, glass formula and coatings. If you're interested
this is a pretty good background on lens formulae for normal lenses.