You can very much trust it. Mostly, that is. The issues usually occur when data flows and physical flows get disconnected. No way blockchain will solve that.

Most companies aren't completely aligned with all their suppliers. Just look at Apple trying to root out child labour. A formally verified supply chain has some limited use cases because you can prove some pieces aren't lying to you (e.g. that you're actually not sourcing your parts from conflict materials, and they are coming from somebody reputable).