I did not read the other site's post were that statement was made, but I would think the supposition would be comparing two cars equal in all other aspects. Gary, you seem to have "muddied " that reply by comparing an untouched original ( w/out paper) vs. a restored (w/paper),IMO.
The only thing I can think of were the documented non OE drivetrain trumps the other is in ease of selling. It is easier to just flop out a paper and say, see, it is real 'cause the paper says so as opposed to going through a lot of vetting by others (particularly if one buying is not well versed in authenticating) to insure the car is what is claimed.
This is not as much a concern to the avg. CRGer because, 1) they generally view the car they are buying as a keeper and not selling(but we never know what tomorrow may hold?) ,2) our confidence in our own authentication abilities and knowing who and what to ask gives the avg. CRGer an edge in not having to have a piece of paper to prove what we already know. Kind of reminds me of a college degree. I knew I knew what I knew, but an employer needed that paper as reassurance. Same with a dog. You can witness 2 of the same breed w/papers, I'll ad, sire a litter. You know the litter is pure bred, but without papers, no one else will know? So, it comes down to one's own confidence and one's purpose (not intending to sell) IMO.
Personally, because of my own level of knowledge, a born with drive train is more desirable than non B.with, An Untampered with (engine never been apart) even better, long ownership with early pics and history, even better! So, lots and lots of factors to an enthusiast over someone only concerned with can they unload it if needed.