Salwico n-38

Hello,
I am doing some research on Salwico nic-38 smoke detectors and I’m coming up with a dead end.

All I know is that they stopped manufacture in 2005, and have replacements in kind for the application if one fails.

Is there any way to check the born on date for the detector? They are ionization and I think they should have a 10 year shelf life, but can’t find literature stating such a fact.

Thanks