I'm not familiar with the history of the act in detail, but my understanding is that neighbouring rights is a relatively new concept in Canada and that exemption was introduced at the same time as the neighbouring rights regime. I may be incorrect about that, but that's my basic understanding.
I don't think there was a neighbouring rights tariff prior to the introduction of that portion of the act. Certainly, campus and community radio stations were required to pay other tariffs prior to that, for example, to SOCAN. I don't think there was a tariff for neighbouring rights earlier. My understanding is that it was introduced in the late 1980s or early 1990s.