I did some investigation about the results from the /who command.
I logged onto 5 of my wow accounts on chars in my guild and tried the /who command.
I found that when a char logs-on then that char will always get the same /who results whether they are grouped or not, in the same zone or not, or in the same shard or not.
My chars consistently got back one of two sets of possible results.
Maybe the /who server hashes your player’s name and uses that to choose which one of two possible sub-sets of the population logged-on that it returns, up to max 50 results.
So with a basic /who search (no filter arguments), one char might get half of the current zone, but another char in the same zone will consistently get the same results or the other half in that zone.
So 3 of my chars would get the same guild/zone set of results and the other 2 chars would get the other half, consistently, no matter what location/group/zone/shard they were in.
Same with a /who guildName search, one char will get one half of the guild online and another char will get the same half or the other half of the guild list online, always, but never the full guild online list.
The n- name qualifier does not work at all. The z- zone qualifier only gave me half of the zone population , or some consistent random sample of the zone population, up to a max 50 results out of the population in the zone.
However if i use the g- (guildname) qualifier, eg /who g-guildname then i always get the full list of all the guild members online.
Also if i use the x- (exact) qualifier, eg /who x-playername then i always get the full details for that logged-on player, even he is a low level char like lvl 4.
Use the /who g-guildName command format to see all chars online for a guild.
For checking a specfic char, such as a guild applicant or even low level chars below lvl 10, use the /who x-playerName command format, it works!
This avoids the /who bugs of getting half-of-the-guild-only results or often getting “0 players total” results!