Depreciation schedules on three properties came back with two different useful lives for the same roof type

Yeah this happens more than people admit. The 15-year classification is almost certainly your CPA treating that second roof as a land improvement or possibly a qualified improvement property under the TCJA rules, which can pull certain components out of the 27.5-year residential bucket depending on how they're arguing the cost seg. The problem is that without a written component breakdown attached to each return you have no way to audit your own schedules year over year, and most CPAs who do this volume just aren't documenting their reasoning in a form the client ever sees. $1,140 times seven properties times a compounding error rate is not a rounding error anymore. I'd sit down with all seven schedules at once and build a simple table: property, component, placed-in-service date, useful life assigned, cost basis. Took me about an afternoon to do this for a client's portfolio last fall and we found three mismatched classifications that added up to about $8,400 in first-year depreciation that had been left on the table.

The $1,140 gap across seven properties is likely closer to $8k once you add it all up.

Cost segregation study on just the roof line items would surface this fast.