Can I be issued a ticket without being pulled over?

I recently got a ticket for my registration being expired (I had no idea it was, I've moved multiple times and everything's been a mess). When I went to pay this ticket however I found out I had 3 other tickets from the past two months for registration. Problem is I NEVER got pulled over and NEVER received any tickets nor did anyone at my previous address. A. How can they issue tickets without actually alerting you to what you're doing wrong? B. How did nothing come up at the DMV when I registered my car or with the cop who pulled me over that I had all of these tickets? If I'd known, I would have happily taken care of everything months ago.