The first 3 digits of the card is usually the casino where the account was initially created.... However if a guest had more than one account created they can be combined into one account.
For example if Jonathan Smith initally got his card at Lake Tahoe he would have one number. And they signed him up as John Smith at Lake Charles he would have another account. Mr. Smith could have his accounts combined into 1 account... usually the account with the least amount of TR points is combined into the bigger account... which means Mr. Smith's new account could either have a Lake Charles # or a Lake Tahoe #.

Hope this helps.