The stations signing HB/ in fact were using a wrong prefix, as the CEPT T/R 61-01 explicitely states the prefix HB9 has to be used. The CEPT novice class has to use HB3/homecall according to CEPT ECC (05)/06. So HB is wrong in any case.
The unfortunate SOTA association prefix HB for Switzerland promotes this error as discussed in Invalid prefix HB
73 de Michael, DB7MM