@AMDG As for invisible structural issues, that's something that no one can predict. But the guy who built your mask will be able to tell for sure if it's got any issues.
As for expiry dates on masks, it's like a lot of other things out there including car seats. They don't expire per se but the liability for company in the event of a failure is absolved.
I would highly recommend changing the foam (either thru Michel or if you want DIY EcoProFoam and Resilient Foam are 2 options). Then it's really up to you about a new lid