For digital sales? Yes, one of the things I like about Nielsen BookScan is it includes probably the best full view of sales numbers, including digital sales, anywhere. At least on the full edition, the cheaper version only includes retail sales. One stop shop for data junkies. About the only data it excludes are direct/direct digital sales, unless the publisher reports them. For example, an ebook bought on Amazon and certain other marketplaces are tracked - numbers from the publishers website may not be. A lot of publishers like to keep that number close to the vest. Likewise, audiobook sales and foreign additions are left out entirely - some authors/publishers make a fortune on audiobooks, and some authors are weirdly popular in certain countries overseas. Ideally, a midrange or very popular author will earn out the cost of a new book on those subrights alone - but that's a luxury many new authors do not have.
That also admittedly is just the sales data - there are additional variables on everything ranging from subrights to audiobooks and foreign editions, internal sales numbers/projections, and a dozen other factors, the biggest being just how many copies were printed and how much was spent on advertising. For all I know, the audiobook to Axiom's End sold 100,000 copies on Audible, and both Ellis and her publisher have a nice return, sales drop be damned. On the flip side, St. Martin's Press might have printed 75k hardcover copies and even with an expensive marketing campaign, and barely sold half of what they printed, and are wondering how to liquidate the rest.
It's not the whole picture, but the more of the picture I get, the less and less good it looks.
As for how much an author actually makes on book sales, that depends on a lot of factors, but the big ones are the publisher and the percentages, and of course, the size of the advance.
The Industry standard for royalties to authors is around 10 percent - some are higher, some are lower, but usually never far removed from 10 percent.
So an author earns a couple bucks on each hardcover sold. A little less on each paperback. Less if its from wholesalers. Nothing if it doesn't sell at all.
So lets say Ellis earns $2 for each hardcover of Axiom's End sold... that puts her take near $68,000. maybe another $20k for the new book, and $15k for the Axiom's End paperback, just sop we're dealing with nice round numbers. Gives her around just short of $100k... about what she earns in a month from Patreon. And those royalty checks aren't going to get bigger looking at her sales numbers. Plus, advances are structured so she won't see all that money at once, usually biannually... this why your back catalog is important, because even in an ideal scenario, you get two royalty checks a year from each book. The ones that turn a profit anyway.
Ah, but here's the kicker - depending on the size of her advance, she might not see a single penny of that money. This is why if you're not literally broke, sometimes a smaller advance works to your advantage. Most authors never earn back those big advances, and it costs them in the long run.
This is also where those circulation numbers come into play... even if she earns back that advance, it's entirely possible that the publisher lost money on the books. Especially for book two, which looks to be taking a real dive. And her sales numbers are already cratering to about where most debut authors land, so that initial push may have benefited nobody but Lindsay's pride.