The below is about Lefton from 1976 and before. I do not have a lot of info about Lefton after this date and do not collect it or own much of it.
The prefixes on some Lefton items (for example AR in this case) are an abbreviation for the specific Japanese manufacturer that Lefton imported from. There are many different prefixes and they are well known and well understood. Many Lefton items have a prefix. KW is probably the most common, which stands for Kowa Toki, a high-quality Japanese manufacturer from the past. Other less known examples are CY, AJ, WK, YU, NE, and others.
The suffixes are not really well understood or explained and are not that common, probably explaining, at least partially, why they are not well understood. Most Lefton items do not have a suffix after the number. Sme patterns Lefton sold in both a rose and a violet design are suffixed r or v (I think for obvious reasons). For example your #660v Violet Chintz coffee pot. Some animal figurines they sold in matched pairs are marked a and b, again pretty obvious why. For example Lefton's #1954 Quetzal figurines (a matched pair) are marked 1054a and 1054b. CS is a known suffix on a cup and saucer, PL on a plate. It is my opinion that less than 3% of Lefton items are marked with a suffix judging from my personal Lefton collection.
It is also my opinion that in this case (and many other cases that Lefton items have an N suffix) the N stands for newer. Lefton sold the #1987 Angels of the Month from 1957 to about 1960. I suspect your angel is closer to the 1960 date than the 1957 date. In my opinion and in this case the N mark makes no difference to collectors.
I hope this helps some.
