Actually , the First Edition ADRs were distributed for discussion purposes. However, they were not adopted as a legally binding set of standards under either national or state/territory law. The Second Edition ADRs came into power in 1969 and after 1988 were progressively replaced by Third Edition ADRs.
I'd say by that,
PCV before ADR26 in 1971 was a voluntary industry standard,
By 1968, most manufacturers had PCVs in place but breathing through the oil filler caps
and all had closed PCVs and Carbon Monoxide Idle control settings by 1971.