Scott is just rounding the gauge to the nearest half. The
Classic catalog might have updated the perfs to 11.75 where appropriate.
Standing Helvetias are not like modern US discount postage with stamps from a half century earlier being used for postage. So the 1908 cancel (if genuine – why fake one on this stamp?) tells us that this stamp is from one of the last Standing Helvetia issues. IMO, even 1903 would be too early because of all the issues between that and 1908.
To further confirm that, Wheelman's stamp is the re-engraved one.

Left stamp is Scott 94a from 1901, one of the last issues using the old plates. You can see plate wear and re-engraved fixes everywhere.
Right stamp is a completely re-engraved one, Scott 112a from 1906. Scott perf 11.5, everybody else says 11.75. And it's 11.75 exactly. Scott doesn't explicitly say this is re-engraved, but the note on the stamp (112) above it applies to everything following for that design.
The re-engraved stamp has thicker letters in HELVETIA. Check. It also has larger stars than the original plates. Check. FRANCO is not as steeply angled as on the originals. Check.
Wheelman, yours doesn't look like a granite paper stamp from here so that leaves Scott 112a or 112 as the only choices.
A graduated-style gauge would confirm perf and may be much more useful generally to you at this point in your collecting life. The Scott/Linns ones are cheap, available and work great.