Treaty limits did not cap French submarine numbers

Did the Anglo-American-Japanese submarine tonnage limit prevent France or Italy from building more boats?

No; the restriction applied to Britain, the United States, and Japan, while France used its freedom to field roughly eighty submarines rather than about sixty.

The premise confuses which signatories accepted the relevant limit. Britain, America, and Japan restricted their own submarine tonnage, while France and Italy were not capped in the same way. France therefore built a force of roughly eighty boats against a notional sixty for the constrained navies. The numerical imbalance was a treaty outcome, not a covert French violation.