The Now function expects a pair of moon brackets based on my experience of it’s past use.
In the latest release (as of 10.22.2022), the function is not indicating errors at design time if these brackets are not specified. Here is an example of an expression not showing static design time errors.
I did a basic test to see what the impact is. Here in this image, I have added the brackets in.
The rule shows the right result if the month value on the left is less than the current month on the right.
However, if the brackets following the Now function are removed, there is no error reported at design time, but the validation returns false all the time.