Yes, sickly pale green colour on the plate. Is it not possible to put a plate through a development cycle (under a safelight) and, if it doesn't develop, wash the developer out, dry it off, and make an exposure on it? I don't recall which way round the untaped dark slide was, but I have a feeling it was the same as the other two - I don't remember a feeling of one being different from the others (but I didn't notice that the others were taped, either).

Some photos below of the two taped plate holders. One has been taped up with broad tape, and the other with narrow tape. There is also a remnant of broad tape on the latter, as well as a number, 29, printed (not hand-written) on a small piece of paper stuck under the tape. The camera and 3 holders came in a leather box-type case which is just big enough for these - certainly not big enough to hold 29 or more plates.

The number also repeats, as if it came from a roll of paper with the number on it all the way through. Could this have been applied by whoever supplied the holder loaded with a fresh plate? Would camera owners have bought rolls of paper with printed numbers to do their own indexing of holders? Wouldn't they have just hand-written the number on a label, or painted it on somewhere?

Holder 1, dark slide side.


And the other side.


Holder 2, dark slide side.


And the other side.


Close-up of the number.