how is maint-x.xx updated?

While testing some potential fixes that would apply all the way to 2.17.5,
noticed there was no official "maint-2.17" branch documented anywhere, and
while I could obviously create my own based on the last released tag, it
was missing the following `make test` breaking fixes:

  macOS: 89c0b113a0 (test: correct detection of UTF8_NFD_TO_NFC for APFS, 2018-04-30)
  NetBSD: 5826b7b595 (test-lib: check Bash version for '-x' without using shell arrays, 2019-01-03)

which begs the question; is this something worth documenting?, should we care
about maint-2.16? where is the line in the sand? can whoever is the power to
be make sure if we ever do a 2.17.6 release to cherry-pick those 2 fixes?

Carlo