Help regarding airbag light

Hi, I've just bought a Nissan navara which has just passed its mot. When I took it for a test drive, I noticed the airbag light illuminated, the seller said he'd sort it no problem, and put 12 months mot on it, which I was happy about. When I picked the van up, the light was no longer illuminated and he had mot'd it on the same day as he promised. However, the engine management light came on a few days later so I took it to be diagnosed. He found a separate minor fault but informed me that the airbag light had been covered with tape. Would this have been a fail on the mot?? There is no advisory either on the certificate.
Thanks for your help