Having used Library and Archives Canada for more than a decade it had never occurred to me to ask about the microfilm coding system. Films are in series A, B, C, H, K, M, and T.
Two knowdgeable colleagues have enlightened me.
The A series is material from non-governmental sources.There is also a HBC series for Hudson Bay Company. What are the others?
The B series is from British governmental sources.
The C series contains material from Canadian governmental sources.
I could always do with more education in the ways of LAC, to be shared on the blog.