Tim,
You are a source of much information.
I did know that the ordinance survey maps had large Grid-True differences, but now I understand why.
Funny aviation maps are always Lat-Long and true with magnetic variation lines in magenta.
The old US Army FM (and field practice) was my early exposure or torture ?.
The USGS (and I wonder how much the old DMA is behind it too) is going to give us more goodies, well we will see and hope.
Guess it's better than false N/E in the US Surveyor Foot right Units?