Yes! In fact, we are very interested to have historical data because thanks to it we will be able to visualize population trends of birds for a longer series of years. However, it is likely that you didn't record the observation time of your old sightings and this is a very important information in forthcoming analyses. In this case, please, indicate an observation time from 00:00h to 23:55h on the day you made the sightings. This "code" will tell the experts that will analyze data that observation time was not recorded for that session.