Huh. I just read the spec. Not quite three 'dimension', but looks like exactly what I was asking for: a (reasonably) automatic and transparent record of previous values, as well as timestamps for when they changed.
I'll call this a "you learn something every day" and a "hey thanks @tthun (and @predakanga)"
I'll call this a "you learn something every day" and a "hey thanks @tthun (and @predakanga)"