I've been flying for my living for almost four decades now. I've made a point of never asking for any sort of certification or reference from a previous employer and in one case declined the "kind offer", from the top man himself as a telling rebuttal. It was probably offered because he was fully aware that I could have taken him to the high court eighteen months before but chose to continue my employment. He would have lost his case because he was in breach of a well publicised legal precedent over the same issue. The very nice official letter of accolade I received on leaving the military is stashed away in a file somewhere unused.
I've never been unemployed.
Having said that, I've never acted in breach of any contract I've signed. Two previous employers did, see above regarding the high court precedent.