A Chambers does help, to be sure. Although some of the more common abbreviations can be sourced from other places, it helps to have that single reference: If it isn't in C. (I think there is one other allowed reference that isn't already stated, I can't remember which though -- concise Oxford maybe>), then it's either not allowed or must be indicated in the Preamble what the reference is.
It's helpful to remember that Medieval Roman Numerals are a common usage, as are IVR codes, which explain both of your examples.