wj vs. wj1: more data points from wj?

https://learninghub.kx.com/forums/topic/wj-vs-wj1-more-data-points-from-wj

Everything else being equal, i.e. window, data etc, wj should cover more data points than wj1, since wj could include prevailing points before the window starts, I was surprised that when running the below in "Joins" notebook wj section, wj1 actually contains more data, any reason why is that?

Thanks.