Vlookup result that then will not change?

Bit of an odd one - I'd love some expert help!

We have a spreadsheet ("Spreadsheet A") that uses VLookup to access another spreadsheet ("Spreadsheet B") to find the person in our company responsible for a geographic region.

Spreadsheet A then serves as a record of who handled certain matters.

When someone changes role or leaves our company, Spreadsheet B is updated to show the new person responsible for the relevant geographic region.

How can I stop Spreadsheet A from being updated with the new person's details?

Is there any sort of best practice in this sort of task?

Essentially I want Spreadsheet A to access Spreadsheet B for a name, and then "freeze" and no update any more if and when Spreadsheet B is updated.

A bit of a messy matter, and I'm not sure if I've explained it right, but here's hoping you guys can help.

Thanks a lot.