He states very clearly in the post that he accessed sales figures included in court documents from various lawsuits TSR was involved in throughout the years. Whether those numbers are "hard, objective and concrete" is, I suppose, debatable. But presumably they're coming from the only entity that would know (TSR) and so are at least as reliable as anyone else's data.
The thing is, having worked in courts, and seen a bit of the legal arena, those types of records typically do not make it into the official court record. I don't now how it is in other states, but in Connecticut sensitive financial information is often sealed. The sort of detailed information he refers to is usually passed back and forth as part of the discovery process between the lawyers and not given to the court. They may make it into the court record as exhibits once a case goes to trial, but from what I remember most of the old TSR cases settled before going to court. Also, the courts in CT throw out old exhibits after a certain period of time, 4 months after a case goes to judgment. Space is limited in courthouses, and they cant afford the space to store old exhibits. There are always transcripts of the court proceedings once a case went to trial, but you have to pay a lot for those, and like I said, I thought most of them settled before trial anyhow. Lastly, he could have gotten them from the litigants themselves, but I would assume that any decent attorney would have, as part of the settlement agrement, also gotten everyone to sign confidentiality agreements as to any sensitive financial information shared as part of the case.
He mentions the Dave Arneson cases, where he sued for royalties. I assume the sales figures he says he read were in the Complaint filed by Arneson. A Complaint is a court document that starts a case. It contains alegatons of truth, not the truth itself. The other side of the case files what is known here as an Answer, wherein they usually deny the allegations in the Complaint. Somewhere in the middle lies the truth. If they settle out of court, we generally never find out the truth. We just know the case is dropped and withdrawn.
I did a quick search for cases Arneson was named in which there was an actual decision available electronically. Keep in mind that a lot of older cases are not available electronically, and you have to physically get them from the courthouse in some manner. I attached them below. I can't seem to find anything really meaningful he can use ass reliable benchmark in them. But, it was a quick search. He apparently spent more than just the 5 minutes I did doing this research. Like I said, I'd like to see what he uses for his figures, as well as where he got them, not just a list of sources used.
Again, my experience is in CT. It may be different in other states.
Like I said, I'd love to see his book.