Revere did not change their logo much, once they dropped the “Process Patent” Double Circle logo in 1968, and started using the 1801 profile, and added the pot/pan size. The one change of much significance is that in 1978 they started adding the year of manufacture. As seen in this photo, -78 is placed beside the size. This continued until the 90’s, when they started adding letters after the year. I’ve read that the letters might represent the month of manufacture, but I can not find any evidence to substantiate this, nor does it seem likely. A year of manufacture is common with almost all items produced anywhere, but rarely is there a need for the month. Many items are produced as an assembly, so it is likely their production times span over more than one month.
If anyone has any more information on these letters added to the 1990-99 years of manufacture for Revere Ware, please comment and let me know.