Is insurance supposed to pay for rotted decking when a policy includes ordinance and law coverage?

This past December, my home lost an architectural asphalt shingle due to high winds. Despite only losing one, State Farm approved me for a full roof replacement, since the existing shingles were discontinued and a good match couldn’t be found, as is required by Ohio code.

During the tear-off, my contractor found rot in some areas of the decking and replaced them to comply with building code, as well as Owens Corning’s specifications. FWIW, when I bought this home a year prior to the incident, my inspector didn’t see any signs of rot on the roof decking from inside the attic.

Ultimately, State Farm denied the supplemental insurance claim for $400 in new portions of decking, because rot isn’t considered an insured loss under my policy. However, my policy includes optional ordinance and law coverage at up to 10% of the dwelling coverage.

Isn’t ordinance and law coverage meant to protect me from paying extra on top of my deductible, specifically when additional work is necessary to comply with building code? The decking still has to be suitable to accept the new roofing materials State Farm approved my contractor to use.

Am I interpreting this coverage correctly? And if so, does anyone have any advice in how to get them to honor it? Because I’ve shared various building codes with various adjusters now, and nothing has been enough to convince them to change their minds. They keep deferring back to the rot exclusion.

TIA for any help!