Surely you have a digi tacho card? Thats going to be half the proof you have been driving. Your previous employer should have a copy of your license, that will have the date your test was passed on it as thats when the license is valid from.

If i was in your situation, there is part of me that would suggest having someone report you for driving without license, the police would have to investigate and dvla look into previous records.

Have you been given a producer at any time since passing? Police will have a written record of your license number and entitlements on that too.