Yea, prescription drug manufacturers have little incentives to seek multi year shelf lives. Combined with the slow approval process real time testing is likely considered sufficient.
I think you summarized it well. There is little incentive to test the limits of stability as manufacturers typically control channel inventory quite tightly. I know my company targeted maybe 14 days on hand? So going much beyond 2 years stability didn’t make much sense as most product was consumed well before it expired.
https://www.astho.org/Programs/Preparedness/Public-Health-Em...