I think "dozens" is an overstatement, but 10-20 wasn't unusual. In college, I could have given you the number for a dozen delivery restaurants, easily. Not proud of it, just saying. That's not counting family, friends, services like taxi companies and movie theaters, and work.
How many different area codes did those dozen delivery restaurants and taxi companies have? How many different exchanges? Was each one a unique area code, each a unique exchange? If not, then you're not really remembering unique 10 digit numbers. There's going to be a lot of repeated numbers in there.
