I had a real drop off in INTs about when Bort changed Med coverage and added semi-aggressive last year. It could just be coincidence or have to do with other changes and build progression as well.
To me, it seemed like this was the 1st point where I started to see my guys do weird things, even with aggressive coverage. Prior to this my guys would occasionally get burned when trying to make a play on the ball, but in general would be "on" the dot they were covering even if the catch was made. After this they would do things like give permanent cushions to guys with much lower AGL/SPD, and the now famous keep moving while the WR stops and makes the catch play.
I also wonder if the reduction in ball velocity (and increase in angle) lowered WR deflections. I know last year a chunk of my PDs and INTs were off WR deflections. This might slip under the radar since they didn't show up on the stat sheet as drops since a PD or INT seems to cancel out a drop.