I don't think Mark worked for SBL but he's mates with Scott and certainly used to turn up on some of his videos.
Geoff Chalmers (of this parish) used to work for SBL but moved off to start Discover Double Bass
https://courses.discoverdoublebass.com/courses
I've not done any of the courses from that site, but Geoff is a top bloke and knows his stuff.