OK, so buying new it's a guarantee that the watch will run at a certain spec. But beyond that?

Recently sent my newmark 71 off to Brendan (Webwatchmaker) to get the bezel swapped out, and figured I'd throw my omega mk40 triple date in the box and have him regulate it.

It's not a watch that omega thought could or should get COSC certification, yet upon getting it back from Brendan a few days later, its running at +1s a day. Exactly what I'd asked if he could manage (the mk40 is a PITA to set the time).

Pretty damned pleased. Goes to show that certification isn't in itself proof of a watches superiority over another or should be seen to be of added value. Interestingly that, and the newmark, are by far my most accurate watches. No fancy certificates, just some folk who pay attention to doing things right.