I came across several Pomona dishes that never made it to production. One is a small 11 inch oval plate with the Biggeraux Cherry and the Ingestrie Pippin :

It has a small greyish oval backstamp.
Regular plates have one motif, such as here the Red Currant:

A larger 15 inch platter has the Roman Apricot. Here it is the shape, or rather the rim of the dish that is unusual:

The backstamp clearly states it is a sample:

Another 15 inch platter has the regular shape, but it features four smaller motifs instead of one large one:

It has the Wilmots Early Red, the Hoary Morning Apple, the Imperatrice Plum and the White Dutch Currants.

This platter has no backstamp at all, on the rim are the letters NF. Slightly mysterious, this wonderful platter.