Check nosing overhang and the effective tread depth it adds. Confirm the projection sits within code when the tread board is shallow.
The nosing is the part of the tread that projects beyond the riser below. When a tread board is shallower than the code minimum, the nosing makes up the effective walking depth. The projection itself is capped so it is not a trip hazard.
The rounded or square front edge of a tread that overhangs the riser below it, adding walking depth and reducing toe-stubbing.
Under the IRC, when nosing is required the projection must be between 0.75 and 1.25 inches. It must also be consistent within a flight.
When the tread depth alone is less than the code minimum (10 inches under the IRC), the nosing makes up the effective depth. With deep enough treads, nosing is optional.