Yes, apart from the cascading OS updates through each manufacturer, there are also Google Play system updates which are firstly hidden away under the About Phone menu, and most weirdly of all, they don’t auto install or even notify you of updates.
These are quite important actually, as they are generic app updates that Google rolls out across Android devices, and they get past manufacturers which no longer update some system apps. They also add new features to the Google Play Store and Google Wallet.
They do come out every month, but my experience is I don’t see them monthly on my phone. However, if you leave it too long, I’be seen like three updates in a row that I’ve had to apply, so check again after you’ve applied one.
Interestingly, too, the linked article also gives a link to a page where you can see what each month’s update has brought as a changelog.
See https://lifehacker.com/tech/youre-missing-out-on-hidden-android-updates