When did this change and what else do I not know about?

Ok, when I was a kid on the swim team back in the early 1980s, we were taught that for freestyle, the pull arm begins the pull as the recovery arm lifts out of the water to begin the recovery. This is how I always swam freestyle. But then the other day, I was told by a coach that the timing has been modified. Now, apparently, the pull arm begins the pull towards the end of the recovery instead of the beginning. I should have known something was up months ago with all those catch up drills we were doing and when I heard my other teammates talking about their "glides" and not knowing what the hell they were talking about (as a sprinter, I never glided). Then, I found out that now, when swimming breaststroke, the head is kept low into the water instead of forward with the top of the cap always peaking through the surface. When I learned breaststroke, letting the top of the cap (i.e., your whole head) under the water was grounds for disqualification. Is that no longer true? And last but I'm sure not least, I found out that back flip turns are no longer practiced. Why not? And what else has changed since the 1980s that I need to know about?