My guess is the 12 indicates the hour (24-hour clock). The crew was called for 1115 so it is plausible that between 12 and 1 they had built their train and told the clerk the car order so he could enter the data into the computer.
I's possible in those days their computer systems were constrained by the number of characters in certain files and for a consist the hour was sufficient without devoting two characters for the minute.