GW is supposed to keep track of everyone who has been in the guild for the week, just in case they are owed participation credit in whichever guild they are in by the end of the week. People come and go and sometimes come back to a guild they were in earlier in the week. For some reason it actually tends to keep track for 2 weeks and on rare occasions 3. I don't know why it does that, but has for as long as I can remember. You might not recognize the name if the player has changed names it shows their current name, which is not necessarily the name they had while in your guild.