you could make use of the groups
example
func on_area_entered(body):
if body.is_in_group("group1"):
# code
To each area you add it to a group and then with the valid signal if the area is in the group you want to detect or not
That for me is the best way, but you could also try with the collision masks and layers, with that you would no longer detect the areas but I don't think it is so convenient since it would be very tedious to configure
edit: (admin note) fixed a typo in code example boidy -> body