Dear heshe,
Omshanti. PBKs have been in existence since 1976, but their number was very less (or negligible) for nearly one and a half decade. It started growing only in the 1990s. And PBKs do not organize any public programmes. The Advanced Knowledge is given individually. So, the word about PBKs spread very slowly (especially in the foreign countries) in the past until the commencement of the internet age. The BK Administration tried its best to block all information about PBKs. And whatever information was given by them about PBKs was mostly negative. So, even if any BK came to know about the PBKs through BKs, they would hardly take any step to know the reality of PBKs. It is only when PBKs contact the BKs directly that they come to know about them or through the internet.
With regards,
OGS,
Arjun