Many consider ANSI 3.1 (or 18.1) to deal just with the number of months (or hours ) on the job. As Marlin said the ANSI standard applies to commercial power plants and the ability to perform the necessary functions. 20+ years of preforming job 'A' does not necessarily qualify an individual to perform jobs 'B through Z'! As I've said in similar topics, the RPM/RSO has to make the decision based (hopefully on personal observation or the watchful eye of a fully qualified and trusted subordinate) on the qualifications of the individual. 36 months as 'hatch watch' does not qualify a person to cover steam generator maintenance.
Over a lot of years I've seen individuals that made the cut (on resume) because of time in a DOE, Lab, or even NPP role, but didn't make the cut in the plant. On the other hand, I've seen folks just out of the medical and/or DOD world (time not accepted by most) that matched the performance of trusted Sr. Techs.
Back to the OP, I think the question was how many am I competing against. The 'house' and 'other long term facilities' really don't count if that was the question. 'Available' at any given time, MOO, I'd go with Eric