st_* variables of ctim vs ctime vs ctimespec; is there a history & recommended use?

   After recently finding stat(1) EXAMPLES error (I filed under PR274189 
with patch and reasoning), I was trying to learn the meanings of these 
variables which lead me through reading stat(2) (found by `man lstat`) 
which says it uses st_mtim and provides both st_mtime and st_mtimespec 
for compatibility.
   I didn't find any listed reason for the compatibility otherwise and 
wondered if that is documented somewhere. Is there a recommended 
'choice' for compatibility that users should know to use for code 
portability or is that documented somewhere else inside/outside the 
FreeBSD project that you can point me to? I also presume that 
'compatibility' should be clarified in our copies of the NetBSD 
program's documentation unless the two projects use the same variables.
   Does stat(1) use of st_mtime stat(2) saying st_mtim have connection 
to causing more of these variants or does it use the variant due to 
being a tool pulled in from NetBSD or was it a decision of separating 
programmers and users interfaces with the system?
   My apologies if I should have sent this to a different mailing list 
but I have not seen one with a programming focus and this topic seemed 
mixed as it began by my reading up on /bin/stat to use the tool in userland.
Thank you,
Edward Sanford Sutton, III