I was checking out the Las Vegas Strip Web site & came across the paragraph below. Note that it says...

"On this very site on July 2, 1973, the Williams opened the Holiday Casino"

No mention of the Holiday Queen at all. I would think that if they had ever opened the Holiday Queen on that spot that there would be some mention of it on the plaque. You can click the link below to read more.

Andy - Las Vegas

http://www.lvstriphistory.com/harrah.htm

"Let it be known that this special plaque is dedicated to honor Shelby and Claudine Williams for their notable accomplishments and unselfish contributions to Harrah's Entertainment, Inc. and the entire community of Las Vegas. On this very site on July 2, 1973, the Williams opened the Holiday Casino, the forerunner of today's Harrah's Las Vegas. Since then, the Las Vegas tourism industry and the entire Silver State have benefited tremendously from the couple's tireless energy and boundless generosity. The Williams have touched every aspect of life in Las Vegas, from education to hospitality/tourism to government, and without doubt, their kindness and caring have enhanced immeasurably the qualify of life for everyone. Shelby and Claudine Williams are true "treasures" to Harrah's Las Vegas and the State of Nevada."