Calling it good enough for now in 2021.014. There are a number of unrealistic edge-cases you can make happen, especially speed illegal for a specified altitude but I'm no longer seeing corrupted speed displays and such.
I made matching changes to the shared pascal code in uHCDateTime.pas as well. Side note, I wrote the original code while on honeymoon in 2015. What a wife :).
I've widened that particular buf variable to 360=_MAX_PATH+100 characters (Windows has a quasi-limit on paths of 260 characters) and expect it will result in no more overflow for you.