So there’s a button which allows us to add the cached frames to the back cache, but what would be really handy was a way to bake from the first missing frame in order to avoid those situations where you have, say frames 001-189 cached, then copied to the bake, but you just want to get the remaining frames from 190-200 without having to start again. Is there any way?
Ah yes, I’ll bear that in mind for the future but it’s not going to help me with a smoke sim though unfortunately 
Ah smoke, could prove difficult. Maybe try asking the gurus / devs in https://blenderartists.org/forum/showthread.php?343637-Custom-Build-Blender-Fracture-Modifier
They’d be fairly well versed in what can be done with bakes and caches, maybe even smoke.
I’d have thought it should be possible, after all if you play an animation and it caches the smoke sim, when you play the animation again from the beginning it uses the cached frames and only calculates the ones it’s missing at the end.