Jay ... you wrote, "Although you think it seems unlikely, I would say that there is a 100% chance that either your dates are off or that there were two separate establishments."

Below are photos of both casinos occupying the very same building:

I can't offer better evidence that both establishments occupied the very same building than the photos above.

The only question is when.
It's only logical to assume they didn't occupy the same building at the same time.

"Tahoe Plaza" from 1954 to '56.
"Tahoe Palace" from 1956 to '59.

Harrah's took control of that property to expanded their operation after that.
With all due respect to your records and to Harvey Fuller,
it seems someone has made a mistake.