No, I mean that a single key includes more than one tier due to power ups a character received in a brief period of time.
For example Piccolo, has multiple tiers in his Frieza and Cell saga keys because he quickly grew in power during those arcs, making so that he has 2 keys instead of 5.
The same is for Z Goku, who has multiple tiers for a single key, including pre-training, post-training, kaio ken and so on.
Bardock would have a single key which would include pre-zenkai, post-zenkai and oozaru form.