What Does N1-I Mean? What Does Bc-46A Mean?

I agree with Spruett that they seem like catalog designations.

Can you give us the context in which they were used?

I agree the BC-46a is the cat. number with the BC meaning Bank of Canada the 46 is the 46th issue by the Bank of Canada since 1935 and the "a" would indicate it's the first signature combination for this issue the next signature combination would be BC-46b.
The N1-i is used in conjunction with a cat. number such as BC-46a-N1-i.
The "N" refers to it being a special serial number for some reason or another.
The "1" following the "N" indicates that it's a radar note.
The "i" that follows the "1" tells you it's a solid one digit radar with all numbers the same 1111111, 2222222, 3333333 etc.
The next listed would be N1-ii in conjunction with a cat. number eg. BC-46a-N1-ii.
This is the same as above up until the "ii" which means it is a two digit radar eg. 6969696. The three and four digit radars are N1-iii.
I strongly suggest before you delve into banknotes you first get your hands on a Charlton Catalogue and study it carefully.

Cheers, Bill