I'm not sure about the dual use of the chips at both locations. My guess is that the Sahara Thunderbird chips were made to replace the old Thunderbird rack at the T-bird property only, though the chips could probably be cashed at the Sahara cage too.

The reason for this guess is that Del Webb Corporation had a reputation for running a pretty tight ship, and they would have replaced / destroyed the old Thunderbird chips when they bought the Thunderbird property in 1964. They were one of the first large "legitimate" companies to be involved in casinos. Around that same time, they were building the Sahara high-rise tower, also the Mint in downtown LV, and the Sahara-Tahoe, plus other construction projects as well.

I have a book ("Del Webb: A Man, A Company", published in 1991), with this brief Thunderbird reference (page 121):
"The Thunderbird Hotel was added to the Sahara-Nevada holdings in 1964. The building required extensive updating. Spring of the following year was an expansion of the casino area, the dining rooms, and entertainment lounge, and redecoration of the theater showroom and banquet areas. The corporate offices of the Hotel Group were moved to the Thunderbird."

The photo in the book is of the Thunderbird facade, without any "Sahara-Thunderbird" signage. And I can't find any postcards, dice, matchbooks, etc. with the combined names either. Only the chips. Even this paper coaster (pic from MOGH/Chip Guide) has the individual names "Sahara" and "Thunderbird" on it ... no S-T combination.

If anyone has more or different info, I'd like to hear.