At least with my last order (arrived mid 2019) it still was the case, and I don't think this would have changed. The yield of the production is not 100% so they always have to make a couple of extras to ensure enough good chips remain to fill the order. Since it's an outcome of randomness that can only be guesstimated in a ballpark, often enough some extras remain after replacing rejects.
The number always varies and depends on a couple of factors - total number of chips ordered with that particular design, the type of edge spot (but there seems to be no rule like "the more complex the spot, the more extras", or at least it has exceptions), likely more.
You should absolutely not rely on bonus chips if you want some extras aside from your set so you can replace broken or lost chips down the line. If you want those guaranteed, order more chips. That's what I do at least