Vintage MONO Cartridge Question ?

Cleeds, I don't agree with your gross generalization, but that's beside the point.  The OP seems to want a true mono cartridge, and most of those are going to be "vintage" by definition.  It might be more constructive to direct him to consider one of the very few modern mono cartridges that are also "true mono", if you are leery of "used" cartridges (which I am not).  I think EMT and Ortofon still make new, true mono cartridges, but I cannot name model names.  Then too, there is Miyajima.  Miyajima market a whole line of true mono cartridges, designed from the ground up to be mono.  Also, Miyajima offer a choice of 1.0mil or 0.7mil stylus tip radius, if you are anal about early mono vs later mono and groove width.  

Iopscri, I have no idea why you choose 1962 as some sort of cut-off point for early vs later mono. There is mass confusion on the internet regarding this subject, and I don't believe there are hard facts about dates; each company was doing what it wanted to do, and they were not all in synch back then.

I don't think anyone would argue with you that using a mono cartridge to play a mono LP is superior to using a stereo cartridge to pay a mono LP.    And no one would argue with you about WHY this is true.  I also agree with you in principle that I would rather use a true mono cartridge (one that cannot respond electrically to vertical displacement of the stylus) than a stereo cartridge wherein the two channels have been bridged internally so as to produce a mono output signal.  Some might argue that using a preamplifier with a mono switch is identical in effect to using a bridged stereo cartridge to produce mono, but that's another can of worms.

Anyway, all I can do is to suggest you investigate modern true mono cartridges like the Miyajima, EMT, and Ortofon products.

In theory, the noise generated by vertical motion of the stylus in a mono cartridge is cancelled by adding the positive and negative signals from each channel, in a mono cartridge that was created from a stereo cartridge.  As I think Fleib is trying to say, since the two channels are never a perfect match, the cancellation effect also can never be absolutely perfect.  The same applies to using the mono switch, if your preamplifier has such.  I don't own any mono cartridge, but I do use a mono switch when playing mono LPs, and the improvement vs playing mono LPs in stereo is enormous, most notably in the area of reduced noise and an increase in the width of the soundstage.  From this I conclude that faux mono cartridges might also work pretty well to generate a mono experience, albeit not perfectly.  Anyway, the OP is not asking us to debate this issue.  He knows what he wants.

A true mono cartridge, which has only one coil, can have vertical compliance without generating any noise as a result, if there is no mechanism to transduce vertical movement into an audio signal.

Another issue, I much prefer 2-channel mono over the idea of using only one of two speakers when listening to mono.  Old habits die hard, I guess.  But this is why I personally have no interest in ancient true mono, 2-pin cartridges from the 50s.  (While I am a big proponent of vintage stereo cartridges.)