Does anyone know why UA numbers some of their flights the way that they do.

I recently flew LAX-CDG, LAX-IAD on UA946, IAD-CDG on UA914

SFO-AMS is SFO-IAD on UA914, IAD-AMS on UA946

I never switched to a different hard product and neither did SFO-AMS so why change the flight numbers?

My LAX-CDG was the same plane for both segments, 946 and 914. I had he same seat 21J, so I wrote myself a note before I debarked in IAD. When I boarded for CDG, I read my note to myself.

Why would UA not make LAX-CDG 946 for both segments and SFO-AMS 914 for both segments? They are still direct flights.

I am very confused and I hope I have not confused any readers of this post.