If you are working to a 3RM, then the sets leading up to it should be 3 reps, not 5. I would guess your 3RM is probably higher than what you hit, but you were fatigued a bit. Decrease your reps on bent-o ver rows to 8-10 max, closer to 6-8 on ME day. When you do your horizontal plane on DE Day, then use the 10-15 reps. This is all at first, once you get into things and understand your body, you can see how you react various things.
Since this is designed for someone doing a sport, and I am not would it be feasible to add in some supplementary shoulder work or other exercises on days I'm not doing the WS stuff? My shoulders are lagging.
As long as it is supplementary work, it shouldn't be a problem. Although, Defranco designed his program to cover all aspects. He needs to make sure his athletes are make the most out of the weight room which includes hitting all the muscles. Just watch yourself so that you don't don't affect your main lifts.
Connor, someone wrote an article several months back about doing what you do (dropping weight before a PR). However, that isn't the idea behind Defranco's program.
well go read it again. the WS4SB program specifically does not have a DE day because "Joe" felt that those who were in need of the WS4SB program werent at a level that they would benefit by doing a DE day. perhaps your modifications work very well for you, no ones doubting that, but again, if someone is at the level that they are just starting WS4SB, i dont think its very wise to jump right into changing up the program.
As far as reducing the reps to sets leading up to a PR attempt, I've found that it's a useful strategy to give yourself a little more energy than normal.
One thing you could do with it would be to drop the reps and PR one week and then stick to that same max weight the next week and fill in the missing reps (IE go from one back to three on your pre-max sets).