As a general rule the airlines choose what to feature on their boarding passes in order to assist airport staff and airline staff to explain and direct the customers according to their eligible process. That said, not all airlines feature these codings such as “OSS” - but the flight and its connecting customers may still be eligible for this flow. In your case of FCO-YYC arrival, YYC has a high volume of OSS flights and very little Non-OSS. It may seem as though they weren’t scrutinizing your boarding passes when in reality your flight was the only one in the arrivals stream at that time. While the regulations are the same at all airports, how it is managed and verified May differ from one site to the next.