Water Heater label missing

What would you write up for a missing water heater label ?
Other than a possible warranty issue since it is a 1 year old installation.

Age unknown no lable found .
Check water temp and move on. Should be 120 degrees
Roy Cooke

Well I know the age, but since it is warranty inspection I think I should advice the client that his warranty might be shot since he has no serial number etc.

How do you know the age just because the home is one year old does not mean the heater is. That could be the reason no label . I did a home and I took the serial number of the heater when the client moved in there was a different heater there . Very embarrassing to sat the least . I think they got a new heater out of it . Roy Cooke