Think you might be right Leanne - thinking about the use of post as quick or almost-immediate communication in former days, it's unlikely that the message would give the year as the recipient would presumably be getting the note the day it was written, or within a day or two afterwards.
I have postcards written by my great-grandmother pre-WW1, written and posted from London in the morning, to let recipient know she would be arriving at their home that evening! Obviously telephones were either not used much, or few and far between.