The explanation here is that v6.6.2 included some under-the-hood changes aimed at improvements down the line and these bit some users. Eastgate responded quickly with a new build - actually 2 as it turns out.  For 99% of folk 6.6.2==6.6.4 but either way, just update. There are no new features just fixes.

Updates. vN.X.Y. Generally bigger features tend to do into the 'v.N.X.0' releases and the .Y' releases fix/polish those and previous features.  however, stuff also gets added is response to particular users needs (as I can attest) and Eastgate generously sticks those in the next X or Y release. Things aren't held back, which chimes with the licence model based on time - no waiting for a new pay-for update.

I generally have an aTbRef update out on the day or within a few days (disclaimer: I'm the sole author of it). Admittedly of late there's been more lag as PhD deadlines have taken priority. I don't generally record fixes because my experience is folk who have a hot-button issue test that first for each new release: either it's fixed or it isn't.  Fix lists make hard reading. BBEdit's are exemplary in their depth but are actually not that informative as there's so much (often affect 1/few users) the finding what we as individual users would regard as relevant can be hard.

Backstage members have access to the 'Notes.tbx' which equates to v5 and older's 'Release notes' as packaged in the app. In truth, for the casual users it's confusing reading as it's written more for the app author as a reminder and for experienced users/beta testers.

TL;DR - look at aTbRef and the Help 'Recent changes'. If still with questions on a specific topic I'd drop a question to support via email.

You'll usually find detailed release notes in Tinderbox Help.

In this particular case, the fixes were hard to describe -- annoying little misbehaviors that involve side-effects of experimental features. Explaining what was wrong would have been harder than simply fixing it!