I don't have the the alternative source that ultimately matters here, no. But my point wasn't that Cots' estimate is a bad one. It's that you are putting a gospel amount of stock in something that only needs to be less then 1% off to completely negate that proposed budget hard line, and which indeed represents a margin of error Cots has certainly been off on previously in regards to all those complicated 'extras' that go into the final tally figure. To my knowledge and since I started following it 10+ years ago, those beginning to mid year estimates have never been a "to within a couple 100K" reliable.
Which most of the time isn't really even a projection issue at that, since conventional wisdom in these cases would usually draw the conclusion that from a more logical standpoint....the Sox would of never spent themselves that close to a LT threshold entering a contending season that they had every intention of avoiding in the first place. But I guess having entered into the bizzaro world where the Sox are now MLB's new albatross spender, and outspending the MFY by $70m at that, has messed with a lot of long standing and default narrative foundations.
The only figures that are an estimate are the benefits number and the amount paid to guys who spend most of their time optioned to the minors rather than drawing full big league salary. But as those estimates add up to only ~$17M or so (per Cot's calculation), to be off by even 5% is still less than a million dollars.
As for your bizarro world, we are in a whole new world. The secondary threshold the Red Sox are up against is something entirely new, at least in the sense that it is no longer purely money at stake. That changes the equation significantly if we're going to compare to past years.
In past years, the Yankees and Dodgers have both spent far more excessively relative to the tax threshold than the Red Sox have so far this year, but their penalty was only money. It didn't really impact anything beyond the owners' bottom line (and we all know that they, including the Red Sox ownership, have cash to burn), whereas now it impacts future years via the draft and international signing bonuses. For a team in the Red Sox position, marginally increasing their chances of a World Series now is not worth impacting the strength of the farm system in 2020 and beyond.
But hey, maybe they'll go ahead and do it anyway. I choose to believe that will happen when they actually do it, rather than expect them to do it and set myself up for disappointment when they don't.