Why isn't the year printed on boarding passes along with the month and day?

I found a couple of my old BPs in a book yesterday but I can't tell when they are from. The origin and destination are places I fly at least a couple of times a year, but the connecting city is one that is no longer available for that pair.

No big deal - I just wish I could tell what year they are from!

(I searched for a likely FT thread that would answer this question and couldn't find one. I also tried a web search and came up empty.)