Seats and Swaps

Dear, 

I had a question about Seats and Swaps.
I keep getting different answers from the company I purchase the licenses from

We have 15 seats and I understand you can do 2 swaps per seats a year
can you do a max of 2 swaps per seats or can you do 30 swap Seats independently from what seat it is?

How do I know if the seat can still be swapped? do I get a warning from the system saying "if you remove the current user you are not able to add a new user"? Is there a way to check how many swaps have been done for what seat in the year?

The year for the swaps is this a calendar year or each year when you have to extend your license?

Thanks much for your time!
Enjoy your day

Best regards,

Eun