Which is not "in accord" with Solow's account. Leaving after a morning of shooting isn't the same as "the morning he was scheduled to begin work."
"HERB: ...the morning he was scheduled to begin work, November 16, 1966, John Drew Barrymore disappeared, ignoring his role, his moral obligation, and his contract."
It is in accord. You can't disappear unless you have first appeared. Brown's "after lunch" phrasing might be incorrect, but both accounts indicate that Barrymore reported to the studio that morning. Both accounts might be wrong, of course; I wasn't there.
already corrected your error here, but you might also consider Justman's account of Desilu's grievance (through SAG) against Barrymore. The actor's feeble defense was one of forgetfulness, which led to him being barred from work for six months. It's believable that he might have forgotten his obligation and never shown up (though this was unprofessional, and he was suitably punished). It's not believable at Barrymore showed up for half a day and then forgot he had to complete work on the episode.
Inside Star Trek has a few mistakes and hazy memories in it -- enough that I have thought about addressing them in a short article -- but this is not one of them. Brown wasn't there, Justman was, and the archival record supports Justman's version. QED.