As shown by H. Mutzafi in Leshonenu 80:3(2018):284f., the BT forms are not just errors for blm. Rather, as shown by NENA, it is a portmanteau of blˁ and lˁs > *blˁs, with elision of the ayin.
Page refs. in other dictionaries:
DJBA: 221bDrower/Macuch: 66aAudo: 1:79