In standard quorum 2, tasks check each other (distributed both within a short time of each other). When going through the _0 Zero Redundant quorum, then Inconclusive, i.e. the _1 job send out after the _0 completion, the verifier _1 job checks the _0, since the verifier job will be done by a realible (R++) device. Practically though, I think the _0 is then also used to also confirm _1 again. After their verification, the outcome could be:

error-valid (very unlikely)
valid-valid (most often)
invalid-valid (not so often)
inconclusive-inconclusive (3rd copy _2 send out, and a situation also occurring with upfrnt quorum 2 such as with HCMD2)

probably a few other combo's are possible.

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edit: Title "Validation" :D
edit 2: The first in a quorum to be sent locks in the platform (Linux/Windows/Mac) all wingmen/repairs are run on. Observed, _0 does not always go out first. Received recently a _1 when the _0 was still sitting in "waiting to be sent", the servers probably waiting for the fitting device to do a work-fetch call.