I recently had a baby and had planned on sending announcements. However, eight weeks have already passed. Is it too late to send mailed announcements? I have already sent an electronic announcement. If someone has already sent a gift (so clearly they know), is it still appropriate to send them an announcement? 

It is not too late to send your announcements, but if you have already sent electronic ones, you would not repeat the announcement with a mailed one. One announcement per household is all you should send. You do not send announcements to those who already know your happy news and who have already sent a gift.