I think this is where the communication is failing on my part.
Do you mean over the year, you identify changes you would like to implement at a future day but you don't actually change the existing contracts or introduce the changes until a set date (December) when the new contract is issued to be read and signed?
If so, that's a whole different situation to changing the contracts throughout the year.
I think you are just identifying changes and updating your own master version of the document not changing the contract as in the legal agreement between two parties?