[derefr]

Thinking about this, that's basically equivalent to, in America, handing out your American W2 tax forms instead of references. The forms give a duration for which each company had you on payroll, plus a separation code (layoff, quit, fired with/without cause) if you're no longer there.

Sure, they also show how much you were being paid, but presumably you could wait until after a salary negotiation to hand these over.