The new CBA didn't do any favors to the Celtics. Last year, they had two 8 figure expiring deals that they couldn't do anything with because the new CBA outlawed "Catch and Release" transactions, and now Pierce can't come back here as a FA if he's traded and his new team doesn't exercise this option next season and make him a UFA.
I guess he could not sign with anyone for a year and then sign with the Cs after the trade deadline in 2014, which would satisfy the one year requirement, but would be unprecedented.