Trip ID's for SCHEDULED trips in GTFS-RT always correspond with the trip_id values in the latest GTFS Static file for LIRR, as required by the GTFS-RT specification. They are merely internal/matching identifiers, and not meant to be shown to riders, parsed to dissect underlying values, nor for any other purpose. We reserve the right to change the format of the ID as needed by changes to our underlying systems or any other reason, without notification.
If you need the train number, please use the trip_short_name column from the static feed.