In saying this, a language connection or genetics connection (R1b) Frisians are R1b-U106/S21 is a possible way to find that connection.
The genetics could have been bred out, be very scarce within a small area or gone by now though imo. Language however could have stayed as a language of the sailors/traders, a common language for cultures to take on, like Phoenician/alphabet became, since the Frisians were sailors too and also knew the way back and forth it seems, just as they knew where Atland was.
If they knew whwere it was, is the location stated in the OLB? (i havent read OLB fully ,therefore i am asking)
Other than in the OLB (and in the works of Olaus Rudbeck in the 18th century), Was the name Atland in use medieveal times ?