References are normally requested to the company, it is not normal to have a letter in hand. This is true for non-aviation jobs and aviation jobs alike. If I was interested in hiring someone and they produced a letter from their previous employer....my first thought would be ...Yea right....and I would then contact the employer directly.
Really confused as to what the issue is and in agreement would ignore a reference handed to me.
If you leave an employer your next employer MAY make a request for a reference from a previous employer.
Reality is that as a result of legal claims because an employer said what they wanted to say an employer is under restictions on what they can say.
Many employer references now just indicate
"John / Jane Doe was employed by X Company from April 1st 2010 to December 31st 2015."
That is it because it is FACTUAL.
As for Personnel records on what an employee did during the time at a company they are owned by the company not employee.