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For some it does and for some it does not.
What seems to be the case (seems underlined) is two issues:
1- The lens coating difference......
2- While it is the same optical formula, many question if it is the same glass quality, bearing in mind that glass for all lenses of all manufacturers is produced in batches and.......etc
We are splitting hairs here as to whether the Chateau Margaux 1956 is better than 1957.....you still need to find the guy who tasted both....
Teasing answer Almass
Good wine depends on wine maker`s skills and vision.
50mm f/2 Summicron-R I produced till 1975 was a genius design of Walter Mandler. So were next versions: v.II non-ROM and v.II ROM version, which as Almass mentioned differed in coating and was co-designed with Garry Edwards & Erich Wagner (1977 design inputs)
As for Canadian or German `versions` - I don`t know if there were versions differences beside ROM, which was produced only in W. Germany. The ROM version costs hefty premium as Milkman mentioned, but mainly for such reason.
Milkmanm you may want to download free, older PDF version of Puts` "Leica Compendium" for more info.