When do we count a match as a success? Does EH have a specific definition?

Can we say that a year's solid committed relationship is a success? Six months? Does it have to become a marriage engagement, or marriage? Does EH consider cohabitation over the long term a success? What do we define as long term?

Should we wait until a marriage has survived a certain amount of time? Three years? Five? Ten? Thirty?

I'm not trying to be a smarty-pants here, just curious as to how EH defines success (I think all of us - the customers - have the "I know it when I feel it" in mind) when they do their internal reports and planning.