How to find an HP65 missing serial number

[albertofenini]

Hello everyone

I have three units which are missing the silver label in the battery
compartment with the serial number printed on, yet are older than those units where
the serial number was on a label between the two bottom rubber feets

Is there any way to recover it ?

Any code on the Hybrid or on the other ICs that can reveal year and week of production ?
If it can be of help I can post pictures

Thanks for any advice, take care Alberto