Be'lal was a lawyer who switched to the Shadow before Demandred (who was the last meaningful close ally of LTT to do so, mid-war), and we know Callandor was built late in the WOS when the industrial capabilities had already been seriously undermined. This isn't some AS corrupted knowledge, the explanation comes from a Jordan Q&A.

It seems unlikely Be'lal had any aptitude with *angreal, or he would have made a career of that.

We don't have much to go by... san'angreal seem to be a more complex form of angreal. They quite possibly start from a Seed too, perhaps require a circle where an angreal is made by a single person, weakening his/her ability for months. Going from RJ's partial clues, the making of a san'angreal also require some more hi-tech procedure than filling a Seed for months, one for which the AS barely had the capabilities by the end of the war.

It seems likely one of the Chosen managed to sabotage Callandor during its making, but there's no good reason to believe it was Be'lal and not a specialist of *angreal whose little secret died with him without any of the thirteen ever learning of it. There were literally hundreds of thousand Chosen in the AOL - half the Aes Sedai had joined their ranks.

47 Chosen were ever given "officially" the use of the True Power, at least as far as Moghedien knows. That doesn't count for much when you know tons more Chosen might have been granted the same secretly by the DO, for all we know.