The letters correspond to year/month it was born and the little envelope with the two empty casings have the test fired date on them, when it was cleaned and put into a case for sale.
There's a thread on that 'other' forum where people pasted their letter codes and their test fire dates and somebody manages the thread and updates the OP when folks submit their info so others can use it as a reference.
The last posted #s, doesn't seem to have anything newer:
RAA - G-27 - November 2010 - 2.5 Gen. - Blue Label with new half height label, new matte gray slide and gray barrel
RAB - G-30SF - November 2010 - 3rd Gen. - White Label, Fixed Sights
RAE - G-35 - October 2010 - 4th Gen. - Blue Label
RAE - G-35 - November 2010 - 4th Gen. - Blue Label
RAM - G-26 - - 4th Gen - Austrian marks
REA - G-34 - December 2010 - red label
RET - G-27 - - 4th Gen - Blue label - 3 mags - night sights
So with RYP your gun was most likely made in mid-late 2011.
(sorry, don't have a link, I use an iPhone app for that forum too).
That "mujglock" link is for decoding proof mark dates, not serial number prefixes. Some Glocks were made in Austria, and proof marked to be sold in Europe. There were a few times where demand was outpacing supply in the US, and Glock shipped some guns to the US which had originally been made for sale in Europe. Those proof marked Glocks will have a three-letter code on the barrel which is different from the serial number, and that's the code that you type in at the mujglock website.
The serial number list you quoted from hasn't been updated in over a year, I think the serial numbers are up to like SST by now.