Determine iCloud account used for Activation lock?

Have a couple of corporate owned devices that are activation locked to old employees. We've since purchased ABM, but at the time these devices were rolled out, record keeping was pretty poor. It appears they did use corporate email to create their AppleID. Activation lock message only shows first letters of email e.g. a*****@b*****.uk, but the letter in the domain part matches our corporate email domain, so there is hope that is the email they used.

Is there any way to find out the full email, so we can recover the AppleID and remove the lock?

We currently can't find the proof of purchase for the devices in question, so we can't go down that route.

Thanks