Once again thank you for the help.
However, I cannot imagine PA being an imaginary lot number but do not have the experience to judge correctly.
Could one of the experts perhaps advise?

Also I just noticed that the numbers in the lot number from PA may not necessarily be year numbers but may be something else, e.g. plant codes or area sectors. In the ex. below lot number is 88 but year of production was much earlier.

Please note following link for PA lot number. https://www.worthpoint.com/worthopedia/vintage-1949-picatinny-arsenal-20-mm-1876023277