it will need testing in May 2017, and no you don't need a test certificate, when it gets tested in 2017 the test station will put a label on it saying it's been tested.
If the bottle is not marked then I won't accept it for fills at our events
If testing is due I want to see the Pi mark, test date and IDEST markings to validate the test
I would not be happy with just a certificate even if the serial number matched