Originally Posted by DocsMachine
The pre-2001's serial number starts with "599" and has nine digits in total just like the above photo of the Equalizer. That tracks with at least the first three digits being a date, as this PGP could very easily be a '99 model year.
I was told over the phone by a sheridan customer service guy a long while back that on pgps the first three numbers are indeed the month/year the marker was made. It more than likely applies to the equalizer as well. I didn't ask if this applied to the revamped post-2k pgp as it didn't exist yet.