Divorce!
1.) 1920s: All Mona, all the time. There was a lot of jumping between the two personas in the years immediately prior to this, but once women officially had the vote in the U.S., Divorce made the jump to Mona and hasn't gone back to Desmond for more than a brief thing here and there 'til this week. Chances are the Mona was actually working in Washington, D.C. at this time in hopes of swinging votes and hearts and fidelity alike. 2.) Victorian Era: Desmond! He loved this time period. All that repression spun out into some pretty racy stuff. Knowing Des, he was living in California at the time. San Francisco, I think. 3.) Two months before NYC: Still Mona. ... Actually, I think she might have been in Nevada. Huh. This was probably about a year ago, but she would have traveled quite a lot, too.