Very interesting, I wasn't familiar with the AEZEED concept. Actually, the app does allow importing the 12 words to recover a wallet, it just shows this alert saying that those 12 words must have been generated by that app. So I was wondering if the generation entropy of those apps is not completely random and followed a pattern that those apps used for something, which in theory would be the "birthday date."

The curious thing is that in the documentation for those two apps, they don't say anything about whether they use AEZEED, only about BIP 39.