It is a possibility with AOS. The region is not important for OC (or anyone really), what matters is per country limit - none of the OC countries have enough selectees for that to matter - or total limit, which is the only thing that will make a difference for an OC AOS. We did have a few cases in one year, a few years ago, where visas got exhausted near the end of the FY and those cases still waiting for AOS lost out. That said, it’s rare. One factor you might want to try figure out is whether your FO is one of those that tends to batch interviews near the end of the FY regardless of CN.