They have. In most cases the file format is forward compatible, and often backwards compatible, but IIRC with 2.8 there is quite a lot of new stuff that isn’t backwards compatible.
With the development pace of Blender you’ll find a lot of new stuff gets added over the years even between minor versions.
I hadn’t heard of Kaitai Struct yet, sounds like something to investigate. .blend file format of Blender: C# parsing library and .blend file format of Blender: Python parsing library look like most interesting ones.