I was a FAC in the 1990s and there was no strict currency requirement that I can recall. Possibly if you went longer than 6 months, the Bde FAC had to check you out again.
I was in a place where I controlled so often that it never really came up, in my case. Once I stopped controlling, I stopped for good.
I had a pretty good variety of air frames under my belt- T-33s, CF-18s, A-4s, A-10s and F-16s.
I saw a B-52 strike, A-6s and AC-130s, but none of those were my missions.
We only controlled during daylight hours in the old days and it was all done with voice comms.