The ripening wasn’t at exactly the same time. The inherited tree was most likely bought at a big box store or general nursery, that’s why I assume it is just “Green Gage”, or at least labeled that way.
The Althan’s is from a branch I grafted onto a peach tree. I may have Oullins on that as well as another gage, maybe Catherine, which never really got sweet and ripened later than any of them. It may be that roots affect the relative ripening. Our weather has been unusual as well.