This is a security measure. It insures that an unauthorized user cannot tell the difference between a case where an account exists and when the account does not exist. Password prompting always occurs regardless if the account exists. Domain SID, User ID, Global Groups Memberships, Logon Time, Logoff Time, KickOffTime, Full Name, Password LastSet, Password Can Change Flag, Password Must Change Flag, User Script, Profile Path, Home Directory and Bad Password Count. Guest account only matters in the domain of the Server you are attempting to access.
Guest accounts on trusted domains never come into play.
All steps above assume Global Account unless specified as Local Account. The actual internal process is more complicated than the steps described above. This does not cover the actual pass-through authentication mechanics. This article does not detail the internal workings of the MS Authentication Module. The above model assumes that the Guest Account, when enabled, has no password.