If the sum of 19968 and 22235 is expressed as 0063, and the product of 20108 and 19977 as 0362, then how would the difference between 20845 and 20116 be rendered?

In response to Ady's and other comments:

1. This is a d2 problem, don't overthink/work it.

2. The solution involves two codes (a five-digit one, and a four-digit one, the object of which is not secrecy, but the opposite; in fact both codes are in enormously widespread use.

3. The title is a quotation and is a clue where to start looking for the second code.

I'll be back with another clue if people are still stuck tomorrow.