One year, I got a notice that the subscription to one of my favorite magazines was about to expire.  So, I renewed it for two years not realizing that I still had two years left on my subscription.  But, instead of adding the new two years to the existing two years, they chose to send me two magazines for the next two years.

After two years, I chose to let both subscriptions expire and then start all over with a fresh subscription.  Now, when ever I get a subscription notice, I check the magazine label to see when it really expires.  And, I only renew a month in advance.