Currently, when one changes a password, the older ones are still available by clicking the number displayed right next to the “Password history” label in each entry.
However, this history is polluted with the history of other hidden fields in the same entry, which I find counter-intuitive. As it is right now, it’s more like an “entry history” than a “password history”.
As such, I propose support for individual hidden (“password-like”) field history, so you would be able to see the history for each of your hidden fields individually, and not all of them together sorted by their last modification time.