Upvote:2
The Trenitalia timetable changes twice a year, and the 2019 summer timetable will start on June 9th.
Usually the timetable is not loaded on the website all at once: high-speed trains are available earlier, while regional trains are the last to be updated. This is the reason why at the moment you can find the Rome-Milan trains but not Milan-Lecco.
The complete Intercity (long distance, not high-speed) timetable will be uploaded by May 18th (http://www.fsnews.it/fsn/Gruppo-FS-Italiane/Trenitalia/Trenitalia-offerta-Intercity-confermata-anche-nel-prossimo-cambio-orario-estivo), and it is reasonable to expect that the regional train timetable will also be available within a couple of weeks.