There is no limit to the number you can have on your licence/certificate in either jurisdiction. No references available because nowhere does it say that, but also nowhere is there any limit laid down.
In EASA-land, however, for commercial ops then AMC1 ORO.FC.240 applies, which includes at paragraph (a)(2)(ii):
the flight crew member does not operate more than two aeroplane types or variants for which a separate licence endorsement is required, unless credits related to the training, checking, and recent experience requirements are defined in operational suitability data established in accordance with Commission
Regulation (EU) No 748/2012 for the relevant types or variants; and
Hope that helps!