Could be that there is a small, difficult to measure effect on IS from JS wingmen. There was definitely noise in all the training. Note though many of other secondary skills trained were measured, in the range of +0.02-0.05 per week, so that's the effect size that was reasonably measured. Could IS be smaller than that - maybe.
IS would also be trained by 1v1f and JS forwards, along with smaller secondary training from ID and RB training. Maybe some of the IS increase your trainees got was from that? Could also have some cross training contribution.
Yes, I have done some 1v1f, and some rebounding between seasons. That probably explains it. I have changed training, so I never train more than max 3 weeks of the same training, and 3 weeks only if fouls/injuries made it necessary.
Thank you for making it clear to me.