I would want a re-vetting done ... not least to have it on record should I need to make an insurance claim in near future. Insurance companies don't need much excuse to refuse a pay out .
It's no good the vet saying it will test clear, that's not the point. It's an anti inflammatory drug as well as a short acting pain killer, and it may take time before the inflammation rebuilds to a level that will cause the problem to show again. The drug could easily be gone from the system before that happens.