Because on my end, with >>65 and your quote from >>68 it works:
;Loading "irregex.scm"... done
1 ]=> (irregex-match ">>(([1-9][0-9]{0,2})|(([1-9][0-9]{0,2})-([1-9][0-9]{0,2})))(,(([1-9][0-9]{0,2})|(([1-9][0-9]{0,2})-([1-9][0-9]{0,2})))){0,11}" ">>47,64-65,67")
;Value 13: #(*irregex-match-tag* #(#[compound-procedure 14] #[compiled-procedure 15 ("list" #x1) #x1a #x4c7052] #[compiled-procedure 16 ("list" #x42) #x1a #x4cc47a] #[compiled-procedure 17 ("list" #x48) #x1a #x4ccc42] #[compound-procedure 18] #f) () (">>47,64-65,67" 0 13) 0 (">>47,64-65,67" 0 13) 13 (">>47,64-65,67" 0 13) 2 (">>47,64-65,67" 0 13) 4 (">>47,64-65,67" 0 13) 2 (">>47,64-65,67" 0 13) 4 #f #f #f #f #f #f #f #f #f #f #f #f (">>47,64-65,67" 0 13) 10 (">>47,64-65,67" 0 13) 13 (">>47,64-65,67" 0 13) 11 (">>47,64-65,67" 0 13) 13 (">>47,64-65,67" 0 13) 11 (">>47,64-65,67" 0 13) 13 (">>47,64-65,67" 0 13) 5 (">>47,64-65,67" 0 13) 10 (">>47,64-65,67" 0 13) 5 (">>47,64-65,67" 0 13) 7 (">>47,64-65,67" 0 13) 8 (">>47,64-65,67" 0 13) 10 #f #f #f #f)