What is the expiry date of EEA1 registration certificate

Hello,
Normally the EEA1 issue to EU national to confirm that EU national is a qualified person. But since EEA1 registration certificate has no date of expiry then in that sense what rationale/yardstick which define that how long further it will keep on demonstrating that EU national is a qualified person in order to not send again the treaty rights evidences if EU national wish to support Non-eu national application in future.

Not sure about an expiry date, but I don't think it really matters as you will still need to provide all the info to prove that you're still exercising treaty rights when your non-EEA family member applies for EEA2 anyway.

Not sure that EEA1 has much real value...

But why EEA1 registration certificate which issues to EU national does not have date of expiry? How long it is valid for in a way to not provide again treaty rights evidences again?

I don't think there is a rule for that. Registration Certificate (EEA1) confirms you are exercising treaty right at the time of application. It would probably be dependant on common sense. If this is 2 months old, that fine. If it is 2 years old , probably not. I would just add a recent proof of treaty rights (such as a recent payslip) just to show treaty rights are continuing.