relevance of letters prefixing service numbers

[DITNER, S.M.]

Gents:

1-Can anyone clarify, or direct me to site that would assist in doing same with reference to the letters that appear in front of Cdn. Army service numbers?

I have come across several different letters while researching Commonwealth Grave info.

2- If anyone can give me a credible figure with reference to strength of 1st Canadian Corps - Italy 1944 it might help me sort out conflicting info. I have received....

Thanks