It’s not actually that bad.

IME there at least used to be a difference between 'fresh OO doc' and 'oo doc upsaved from legacy' as far as parsing.

I know when I had to deal with a LOT of excel in 2008-2013, somewhere in that range I gave up on trying to parse the XML (admittedly with the then-rudimentary tools, to say nothing of nascent state of nuget at the time) and just learned how to do VSTO (Visual Studio Tools for Office) as we all had excel installed anyway, and it led to less overall code for the tasks we had to do that involved Excel...