Is it free changes for two trips, or free changes for two changes? If you make one change to a trip, have you just used up one change?

I'm hearing even CO is offering unlimited changes, as long as it's 21 days out, and isn't changing the origin, destination, or dates of travel. That's seems fair, if you booked a connecting flight and a direct flight becomes available, or you booked unfavorable times and favorable times become available.