[JdeBP]

There's a whole story about that, part of which is that at the time terminfo had to cater for old systems where there's a limit on the length of a terminal type name. But the same applies as for a missing kitty terminfo entry. The terminfo database is designed so that one can copy records around, and one can put them in a directory in one's home directory if one does not have administrative access to update the system database.

Debian systems have had an rxvt-unicode-256color entry for approaching 10 years, now. FreeBSD for about the same.

* https://sources.debian.org/src/ncurses/5.9-10/debian/rxvt-un...

* https://svnweb.freebsd.org/base/head/share/termcap/termcap?r...