The way I understood it, the "real" engineer would typically also set things up for the 3 track version, and leave a "second" engineer in the other room, while he sat in the regular control room overseeing the mono during the sesssion. So, to create a situation to illustrate, for something like WHERE ARE YOU?, John Kraus would, besides have things prepared for the mono version he would engineer "live", would also have the stereo mics setup. He'd then leave a second engineer behind the small board in the room where the recording was done for the 3 track version, but would stay in the main control room recording and mixing the mono version "live". Some aural evidence bears this out at times, like things being off mic at times to the point of them being off balance on the 3 track version - for instance, the piano in "Day In, Day Out" on COME DANCE WITH ME!, the vibes in "Brazil" on COME FLY WITH ME, etc. - or actual distortion on parts of the COME FLY WITH ME album, and so on. If that was being monitored by an engineer of the caliber of Val Valentin, and not "just" a second engineer leaving things more or less unchecked after the initial setup, I don't think this would have been left to stand. It sure wasn't for the mono version. Obviously problems like this were more an exception than a rule, but that they happened at all, even just a relatively few times, leaves me to believe this is true.
Now, ONLY THE LONELY seems to be an exception (or at least one exception). Years ago, Chuck Granata told me that he spoke with Val Valentin, who claimed to the engineer the stereo version of the album. It kinda sounds like it to me - it kind of has the character to my ears of an Ella Fitzgerald record of the day recorded at Capitol, which Val did for Verve then (sometimes they'd also record at Radio Recorders, again with Val). I can't quite put into words what I hear, but if you're familiar with the sound, you might understand what I'm trying to get across. I've sometimes wondered if Val just did the old stereo mix, or even both, but I'm *guessing* he really may have recorded the stereo version of this album. Maybe Chuck could detail what Val said better?