If they're regulars then presumably they're ST holders in which case they're listed as sold. Only the clubs (that's every club) know how many walk through the turnstiles, besides the odd occasion like NUFC or ourselves releasing details about cancelling STs that have never been used (or misused in NUFCs case) then we'll never know. I suspect it would make interesting reading.
I know at least two are season ticket holders because a relative of theirs sits next to me. One is aged 86 and he just couldn't make it but it will probably be his last season now.