01
Look for dated evidence
Search invoices, photographs, permit records where applicable, and earlier inspection reports. Ask previous owners or facility staff about known replacement phases, but label recollections as such. A building may retain one original slope while another was renewed. Record dates by roof area instead of assigning the entire roof a single unverified age.
02
Use age as context
Share the history with the assessing slater and ask how it relates to the observed material and component condition. Age can guide questions, but it does not replace inspection of the slate, flashing, fastening, and substrate. If records cannot establish a date, say so in the report. An honest unknown is more useful than a confident number that later drives an unnecessary replacement decision.