Is that true that included NIS maps (+mapname) don't benefit from Automounter variable substitutions

Is that true that included NIS maps (+mapname) don't benefit from Automounter variable substitutions?Or am I missing something?

For instance:

# cat /etc/auto_master
+auto_master
...

# ypcat -k auto.master
/os        auto_notes_${OSREL}

# ypcat -k auto_notes_5.11
notes server-1:/export/notes/5.11

$OSREL doesn't seem to be expanded after the (+auto_master) NIS map is read in.
The mounting fails as:

# cd /os/notes
-bash: cd: notes: No such file or directory

Thanks in advance.