Best Of

Todd-AO was a proprietary wide-screen format by the American Optical company.  Founded by Mike Todd.  Competed in the 50s with Vista vision and Cinemascope.

One reason that we collectors have low interest in 24 sheets is that they are pretty much undisplayable.  They are also quite rare for a couple of reasons.  First, they were fairly expensive for theater owners to purchase and display.  Second by their nature, once used they could not be recycled as they were pasted to billboards.
Smaller sizes were actually rented to theaters by the NSS and were expected to be returned at the end of the run.  Thus many entered the collector market in the mid 1970s when the NSS closed their regional warehouses and auctioned off their stock in pallette sized lots.

Here is your proof.

Movies from major studios (like FP from MGM) always had 24 sheets. I agree with you that movies from low budget studios likely rarely had them.

If you had a still showing a 24 sheet from Bride of the Monster or Plan 9 from Outer Space that WOULD be a discovery.

You have a lack of knowledge here. 24-sheets were a standard size and were made for virtually EVERY movie from the mid-1910s to the 1970s. No "proof" is needed of their existence, but it it were, it would be the pressbook that provides said proof.

What you say would make more sense for some unusual poster, like a still showing a special advertising 40x60, which might not have been shown or mentioned in the pressbook.

I have auctioned tons of stills that show poster images, and since they are black and white, they rarely command much collecting interest.

What has done much better are stills showing actual theater fronts with posters displayed.