How would you be able to identify if the shingles of a roof are Class 1,2,3,4 without having seen the packaging that they came in?
You’d have to lift the tabs enough to look at the information in the cellophane strip. Sometimes it’s there, sometimes not. If that has been removed, you won’t know.
I had told the homeowner the same.
He had two options.
See if the company that installed the shingles knew, in this case he does not know who did the work.
Lift the shingles to see if there is marking, while trying not to cause damage to material.
If dimensional shingles are used, that release strip is on the back of the shingle…it would have to be removed to see it. I usually ask if there are any spare shingles stored onsite if I need to see the ratings.