After experiencing both US and Canadian immigration, IRCC is right up there with one of the worst systems. My GCMS notes say they noticed discrepancies in my absences. I’ve only been out of the country twice, and both trips were for a few weeks at a time with no same day trips.
I can see in the notes that they pulled my entry and exit records, and the dates I provided in my application exactly match what they retrieved. Yet they still overrode the number of days I was outside the country for those two trips, bringing my total physical presence down to exactly 1095 days.
On top of that, their PDF physical presence calculator doesn’t match the application calculator, and neither of them matches what they have in their backend system.