What is the meaning of the letters after the expiration date?
I have found a website that should explain this:
https://datecheckpro.com/2016/09/16/%E2%80%8Breading-food-expiration-date-codes-effectively/
This is what it says:

In coding, if letters are used to signify months, “A” will indicate January all the way to December ending with “L”. Next to these letters will typically be numbers indicating the day and the year. However, sometimes the numbered year will come before the letter. On the other hand, if numbers are used to signify the month, 1-9 will represent January to September, while the last three months will be assigned the first letter of their name, respectively (O for October, N for November, and D for December).
Codes may also be comprised exclusively of numbers typically presented in the standard order of MMDDYY or YYMMDD (e.g., September 12, 2016 would be 091216 or 160912). Some codes also abide by the Julian calendar, which assigns a number to each day of the year from 1 to 365. In this case, September 12 would be 255.