When were the SKX399 and SKX401 made?

It's become common knowledge that for Seiko watches the first two digits in the serial number found at the back of the watch indicate the year (first number) and month (second number). These are commonly and casually referred to as BMBY or 'birth month, birth year". For the month, it is easy to tell as November and December are indicated as 'N' or 'D' and not a number.

The tricky part is telling whether its 1999, 2009, or 2019. You need another bit of info about Seiko on this - the watch maker doesn't make the same models for over a decade. It's likely to be 10 years max for the beater types with some exceptions like the SKX007, which was produced from 1996 to 2018. In the latter case, '6' may refer to 1996 or 2016 (not 1986). and '1' may be 2001 or 2011 (not 1991 or 2021).

 

You can use this information to tell if the info posted about some watches for sale are correct (or legit). For example, there seems to be a proliferation of SKX399's and SKX401's for sale these days. These two, especially the 401, were quite rare and were referred to as Pinoy or Philippine divers watches. Depending on the reference or thread your reading or following, the SKX399 and SKX401 were produced either 1997 to 2004 or 1998 to 2005 (8 year periods). These were supposed to be (unofficial) released only in the Philippine market. Thus, the monicker of them being Philippine divers. To be liberal about the period, we can probably assume that a '6' shouldn't appear as a year in their serial numbers. Why? Simply because these watches were not manufactured in 1996 or 2006. You might just have a modded 007 or perhaps a replaced case back if your 399 or 401's serial number starts with a '6'. 

 

The serial number here starts with '9N'. If we are to refer to either periods I mentioned earlier, this cannot be made in November 2009. It should be November 1999.

The serial number here starts with '04'. This cannot be April 2010 and definitely not April 1990. It indicates the watch to have been made in April 2000.

The '46' in the serial number cannot be June 1994 since the 7002 was still in production at the time. It cannot be June 2014 because the model and others like it already stopped production by 2010 or 2012 at the latest. This means the watch was most likely made in June 2004.

As I said earlier, there seems to be a proliferation of the the 399 and 401. Unlike before when it was rare to see a 401 for sale, I know at least 3 that are selling and for very wide range of prices. Photos can be tricky and one must be cautious of online sellers. So the prices of these watches has gone down where the 399's are now selling easily below 8,000 pesos for an all original watch head and the 401 under 15,000 pesos also for an all original unit. Previously, they were at above 10,000 and 18,000, respectively. I think this also shows how fickle the used watch market can be even for such collectibles like these.

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