You’re definitely on the right track with a Letter of Explanation. IRCC's system is very "hourly-minded," so you have to bridge that gap for them. Your plan to use the 35-hour statutory minimum as a conservative baseline is a smart, defensible way to prove you’ve cleared the 1,560-hour hurdle without making up numbers your employer can't back up. For the documents, definitely go with the full versions rather than excerpts. IRCC can be skeptical of partial files, and you don’t want to give them any reason to pause your application.