How long does it take to determine how many copies of a given book have been sold in its first few days/weeks in the stores?

Commenting on reported sales numbers of Hillary Rodham Clinton’s Living History, Rush Limbaugh argues:

“He’s [Simon & Schuster CEO Jack Romanos] lying about how many copies they’ve sold ? they don’t know yet how many copies they’ve sold. It takes them six months to do audits to pay their authors royalties.”

But in 1993, we just knew how many copies of Limbaugh’s “See, I told you so” were sold, after two days no less:

“By its second day in the stores, Limbaugh’s second book had the biggest early sales of a hardcover book in publishing history. That’s what the man himself let slip on his radio show, and as he says, he purveys only the truth.”

PS: According to Amazon, the hardcover edition of Limbaugh’s book was published in November 1993. The quote above is from December 1, 1993.