User blog comment:Harold Burned-Mane/Tamriel Total War II: Rules and Guidelines/@comment-26103034-20160202155748/@comment-17114085-20160202165728

Depends on what each of the spies is doing. If both my and Dragon's spies are causing unrest in your city, then they'd each accomplish their job and nothing more would happen. If I sent my spy to search for others, then he'd find Dragon's spy in a month.