Making Address changes with Effective Date

I am trying to figure out how the Effective date works in the Payroll for the Address Book>Mailing.  If we add a new mailing address should the effective date always be used?  Our T4's and W2's pull from this and last year we encountered issues when the effective date was not used and that was the most recent address, the T4 pulled the address with the most currect effective date.

Also, does the address date affect what address pulls onto the paystub?

thanks

Pam