The callsigns were rolled out here in order, I was in the 7s, then they did 8s, the original G (GM for Scotland) is now a M (MM for here), Full calls use MØ, M1, intermediate use 2E but up here it is 2M, 2I for NI, 2W etc etc, instead of one letter for the Channel Isles it is U for Guernsey and J for Jersey, IOM is D..
The problem with US calls is, they were originally, a number per section of the country but as folk move plus they do vanity calls now..
Each call is unique...but get confusing with vanity calls as they change every few years due to having to reapply.
Don't start me on locators

anyway, ER1 and chasing a J68