I think you'll get away with once or twice before it turns to complete mush m8, although everyone has their opinion on this.
This isn't necessarily the correct order, but I'm sure they all can catch fish.
Live> Fresh> Freshly frozen> Frozen/ defrosted/ refrozen> semi-digested> bit of cloth dipped in oil > Tinned> cooked, wrapped in cling film and bought from ASDA
The frequency or likelihood is never going to be an exact science, but just what works for you. I've used bait that's been frozen and defrosted several times and caught fish, when guys next to me using live bait have had nothing (and visa versa obviously)