AIUI from others on these forums with knowledge of the rules, 1st is 1st is 1st, unless it is explicitly declassified, regardless of the presence or absence of a 1 at the top of the timetable column for that service. In other words, just because the timetable doesn't say that the train does have 1st class seating, that doesn't preclude that it may have first class seating, and, if it does, then that 1st class accommodation may only be occupied by those with a first class ticket. It may be that my understanding is incorrect, however …