I believe this pattern was used by other places as well. I have a backstamped open sugar from the Roney-Plaza Hotel in Miami Beach made by Lamberton Scammell. Another unmarked plate I also have was made by Lamberton Sterling.
I just took a quick poll of the demitasse cups and saucers that I could put my hands on quickly ( about 45 or so) and found that about 1/2 (that's 50%) of the cups were not marked; but most of the saucers were marked. I don't know the reason behind this; but can only think of the small area to place a bottom stamp on the cup!
I also think that the rim treatment is stock; but when you look at the picture on 259, what IDs the plate is the Logo in the well of the plate for the Hotel LaSalle in Chi-town. Lamberton did the stock plate, as did Syracuse (Viking pattern) and Sterling.
Hey, Dick, all, I obviously was unaware that the pattern in question was used elsewhere (thanks, Helen!), but I guess I interpreted the service plate only as having the fancy seal in the center and extrapolated that the rest of the pieces were plain save for the design. And I say that only because I've seen this pattern (without center decoration) credited to the LaSalle so often.
But then, how often do we see unmarked/untopmarked RR china listed as being the real thing? (Seaboard Air Line's Palm Beach is a good example: Were all those unmarked pieces that we see really used in a dining car?)