Unless it has changed drastically here’s how the OAG works
each week all the contributing airlines send their schedules for the next 52 weeks to the OAG
The OAG then process all this into their systems.
Some airlines only do this monthly (and some only do this at random intervals (like changes of schedule winter/summer etc)
In many cases the contributing airlines are using the returned data (which is every other airline’s schedules) in their own systems to enable through-bookings on other airlines.
Some airlines are only using the OAG to flag their services to the travelling public. These are the ones that are usually not updating their data in the OAG very often. From (ancient) memory this is usually the LoCos (who are not involved in interline traffic).
Hence the reason why Ryanair may be showing flights in the OAG that will not exist in the next season’s schedule; and conversely may not yet be showing flights in the OAG that WILL exist.
By the way, this may well be 110% wrong and completely inutile, but I’ve been out of that loop for a few years...