Even including a couple of outliers, the correlation between serial number and component date is remarkable (r = 0.995 for a 4th-order polynomial curve fit).As DOD's FX100 pedal board (made in the 1980s) required one to remove the pedal's bottom plate for attachment, which could result in the wrong plate being re-installed after the pedal is removed from the board, such a high degree of correlation during this time is especially striking.
This scheme above is for Roland gear from the company's inception (1972), to the point where the numbers recycle in Nov '80, and then on for a second go through the 80s.
The trick with BOSS pedals is that at the time of this serial scheme's turnaround, they were only using a basic 4-digit version of these numbers - 9400 for May 1980, 7800 for January 1979, and then 0500 for April 1981.
One of the outliers is a FX15 Swell Pedal at serial number 408k.
As the FX15 was a slow seller, it is reasonable to assume that many circuit boards were assembled but not immediately housed in an enclosure, which would explain why the component date was about two years younger than its serial number.
So it must have been made when They first moved to Taiwan or one of the earlier Batches.
Some early DOD FX-series pedals have stickers with the date of final assembly, but unlike Boss pedals, the month and year of manufacture is not encoded in its serial number.
At the beginning of 1983, serial numbers appear to abruptly step up to 200k.
We had never seen a DOD FX-series pedal with a serial number between 117k and 200k, until Jeff Kehoe sent us photos of his FX25 (SN 118400).
Five related pedals (represented as red circles, including four Digi Tech PDS-series twin pedals and one DOD Master Switch 225, each of which used the same type of serial number sticker) fit very well with the FX-series data.
Although we only have data from four PDS-series pedals, it may be reasonable to use this plot to estimate the production date of all PDS-series pedals.
For example, we now believe that a pot stamped "2009" is a date code meaning the 9th week of the year 2000.