I encountered only one tiny issue: PROBLEMS has an item titled "I get warnings about special characters in the groff_char(7) man page" that includes sample warnings that don't match the warnings troff currently generates.
I noticed this because when the build threw those warnings, the first thing I did was search PROBLEMS for the warning text to see if it was a known problem (which I was 99% sure it was; this is not my first groff-building rodeo), which of course didn't work with the text having changed. PROBLEMS shows example warnings worded this way: troff:man/groff_char.7:1000: warning: can't find special character '.j' My build generated warnings worded like this: troff: backtrace: file 'man/groff_char.7':1033 troff:man/groff_char.7:1033: warning: special character '.j' not defined The line numbers needn't match, but the warning text should, especially the part that's a likely search string (I at first used "warning: special character"). Luckily this requires only a very small change to a documentation file.
