Reading the datasheet for a USB switch IC, it says "top through view" for the pinout diagram (page 2). It seems like this means "looking from the top-down at the IC", where the notch is in the top left. Is that the correct assumption?
Shortly after writing this, I had another look through the datasheet and found that the physical dimensions on page 15 indicates the position of pin 1. Sharing in case someone else finds this useful.
So, I guess "top through view" means "top down view" or "top view". However, I'm unsure about the significance of the word "through" here as it's an SMD, not a through-hole mount.