Jay, It seems unlikely at best that the Plaza chips would be ordered in 1959 because that was the last year the "Palace" operated in that building and when Harrah's took it over, using that land to expanded their footprint at the Lake.
Might it have been a misprint on the chip order?
All my research tells me the "Tahoe Palace" was in that building from 1956 to 1959.
I have to conclude that the "Plaza" was only in operation for a couple of years before closing and in 1956 that location became the "Tahoe Palace".
IMHO