Pretty much all the outfitters in the BV area run Numbers...except Noah's Ark. Don't think I've ever seen them up there. The companies located north of town definitely spend more time on Numbers (AVA, Kodi, Lakota, Timberline, etc).
As far as when.... I don't think anyone can tell you that. It would depend on your skills, the number of senior, experienced guides working for the outfitter, and customer demands. You can count on it being very unlikely in your first season with a company.
GARNA’s mission is to foster stewardship of the resources of the greater Arkansas River region through education, volunteerism and experiences. https://garna.org