Complex sentence: There were previously a topic of the ISO TC 154 (one of ISO technical committees) and an international standards of addresses, the Physical Addresses and the Article RL 123.3.3 of the UPU Letter Post Regulations, for many years and most countries adopted those specifications.
Split into simpler sentences: There were previously a topic of the ISO TC 154 (one of ISO technical committees). And there were for many years an international standard of Physical Addresses, the Article RL 123.3.3 of the UPU Letter Post Regulations and most countries adopted those specifications.