Why do current transit charts include transit dates from the past?

Older dates are present along with current dates in transits because they are all part of the same transit.  For example, a current transit may include dates from 2012. At that time, it was only the start of that transit.  Events at that time can be profitably re-examined in light of better (and more recent) understanding. Sometimes with outer planet transits that recur over time we say "stop, look, and listen." The first time it just gets your attention.  The next time you look more closely and finally you begin to get the message.