"Things You Wouldn't Know If We Didn't Blog Intermittently."
I recall not getting 16 & 18mm sockets with my sets. Googling, I found a lot of forum posts complaining about things link this, but then lots of commenters saying they had these sizes. Looking at sets for sale, I found a couple that skipped 16mm but included 18mm as the largest size. In my experience 19mm was much more likely to be needed. Anyway, a lot of effort to find this size socket and then risk getting caught by the cashier cracking open the roll.
My thought was that the sockets cost more than $10.
You are assuming they were purchased and not stolen.
The cashiers should keep a magnet handy for a quick check.
So SI sockets are the new wooden nickels. I knew the metric system was bad....