With regard to David Evans' 20-5/8" unidentified discs, while
I can't identify them I think I can help eliminate possibilities.

Criterion and Olympia boxes in the 20+" size did not have such
a large center post.  The sister box, the Euphonia,, however, did.
_But_ 99 percent of all F. G. Otto products had discs made of zinc,
not steel.  I've had maybe a dozen steel 15-3/4" Criterion discs,
but I have never seen nor heard of a steel disc in the 20+" size.

Regina made a 20-3/4" disc size which had a larger center hole.
If you have reproduction discs ("bright tinned") they could be just
a shade off the original diameter.  Most of the European disc boxes
did have a larger center hole.

Perhaps you could send a picture or specs of the discs to Lester
Jones at Renaissance Discs and see if he recognizes them?

Good luck with it!

Nancy Fratti -- Nancy Fratti Music Boxes
Canastota, New York, USA
http://www.nancyfrattimusicboxes.com/