Are there any grubs not present on the Collector map?

I got it. The Collector's map doesn't display grubs that are in areas, for which you don't have a regular map (didn't purchase it from Conifer). For the longest time, I didn't have the map for Fog Canyon, and as soon as I purchased it, the missing grub showed up above Teacher's Archives.

https://hollowknight.fandom.com/wiki/Map_and_Quill#The_Collector.27s_Map

The Collector's Map indeed shows the locations of all 46 Grubs on the map, marked by a pin. It's possible that one of your Grubs is just in a really weird spot. Scour the map! (You can also watch this video and skip to 7:22, where he scrolls through the whole map.)

For example, this one tripped me up on my own playthrough for the longest time:

To save this grub, there's a fake wall you need to break in Deepnest. In my own playthrough I would never have known that without the map.