I'd venture to guess that the reason you nailed those two birds a couple years back was due to the shot being instinctive, and reactionary, no thinking just point and shoot. My wife got a new 20 gauge Rem 1100 from a good board member here about 8 months back,
very first shot with a shotgun, ever, on her first clay she smoked it. Probably had floated to about 40 yards by this point too, and was sinking fast. I figured it was a gonner, but then she snapped it and nailed it with zero instruction except how to hold the gun. All I was hoping for was to show her what to expect.
After that first one, my instructions increased, and she began over thinking it, it became much harder to break clays with all the directions running through her head. Next time I take her out, I won't say a word, I'll just start sending clays up and let her figure it out, intuitively. Over thinking anything, especially with such a small window of opportunity can cloud things up pretty well.
Now, just to throw in some advice and more to think about...

The second most typical miss scenario behind stopping the swing I've noticed with shotguns on clays or birds from people who know how shoot is over-leading. Get to thinking more lead is necessary than actually is, due to over thinking.