COSC...how long is it valid?

You buy your new watch, all SKIPPY because it is COSC certified...

...without service, how long is COSC accuracy maintained?

From http://www.cosc.ch/faq2.php?lang=en :

FAQ - How long is a COSC certificate valid?

The title of chronometer can be compared to a diploma from a specialized school. At a given time of his life, a candidate has proven, thanks to an exam, that he had met with the performances criteria providing him with that title. In the same way as for a graduate, this title has been granted to him for his entire life, although his performances may slightly get altered within the years.

Well they seem to be skirting the question with that answer!

How knows what happens to it before and during installation, shipping, a whole bunch of things can go wrong! All it means is in a controlled enviroment it passed all testing! this is way before the movement has been cased!

Remember that COSC is awarded to the UNCASED watch. SO, that accuracy that it achieved may well have ended on its boxing up for shipment back to the company that submitted it. OR, it may be that accurate for decades. It's all in how its treated. What we do know is that the movement is CAPABLE of that level of accuracy and barring any serious damage ought to be able to be regulated back to that level again by a competent watchmaker.

There really doesn't seem to be a definitive answer with this one !
Like the guys have said, the COSC accuracy can evidently last
for a very short or long time depending on that particular watch.
One might be accurate for years that is treated well. While another
might lose that accuracy very quickly. It seems like servicing the
COSC certified watches often is best. ..On a side note, I just
realized there are COSC quartz watches ! ..Here are a few extra
links related to COSC also..

http://www.chronocentric.com/watches/accuracy.shtml

http://www.prestigetime.com/page.php?accuracy

http://www.timezone.com/library/wbore//wbore631733384647656250