The numbered endings are all fundamentally the same: the only real difference is that they give you different debriefing texts.
The Loose ending, aside from the absence of debriefing text and the different Outro, is fundamentally different from the numbered endings in one respect.
To make a numbered ending occur, ALL the triggers which are of that type must have fired. For example, you may have three triggers, each associated with an objective and each type End#1. The mission will end once all three of the triggers have fired.
To make a Loose ending occur, ANY of the type loose triggers must have fired. So if you had three loose ending triggers, and only one of them was fired, then the mission would end.
In practice, this difference is actually rarely used. Good mission designers tend to use variables to keep track of which objectives have been completed/failed, and then fire the appropriate ending trigger accordingly.
'Win' and 'lose' are very unhelpful words when talking about ending triggers. There is no reason why you couldn't make a mission where firing the loose trigger would constitute a win (for example, by getting to one of several possible extraction points) while the numbered endings could constitute losses. (Out of time, your buddy killed on the way, observed crossing the bridge, etc..) More commonly, End#1 is win and End#2 and End#3 are losses. Sometimes End#1 is a loss because that is the only possible outcome of the mission.