In 1951, Victorinox filed the patent for a new can opener with small screwdriver, following a change in tin can standards.
The "1961 Models" have this can opener, but some of them have a stamp with a Swiss Cross and the letters “PAT” (this stamp lasted from 1951 to, it would appear the 1980s) whereas others have no stamp and the shape of the opener is slightly different.
As we have no specific information on this subject, we simply limit ourselves to mentioning this fact and inform the reader that these two openers appear indifferently on all variants of the "1961 Models".