Some odd custom timecodes set on a number of YouTube video links

[piecesofuk]

I've been working my way through the first few chapters and I've noticed that some of the YouTube links have a time code value set so that the video isn't starting from the beginning. Doesn't seem to be deliberate as some of the videos are starting mid-sentence.
For example, the YouTube links at https://natureofcode.com/forces/#forces-and-newtons-laws-of-motion, https://natureofcode.com/forces/#the-n-body-problem, https://natureofcode.com/forces/#factoring-in-mass and https://natureofcode.com/oscillation/#properties-of-oscillation
It seems that the majority are using the YouTube parameter ?time_continue= and others just ?t= There are a quite a few matches when I search for "time_continue" in the repo.