In any case, inform TTE before boarding.
I didnt make it in-time for Lalquila Express @ GZB & boarded Prayagraj Express, who overtook Lalquila Express & alighted @ Khurja Jn (Prayagraj dont have stoppage, but stop there) & catched Lalquila Express...
Was having 2A ticket for Lalquila & asked TTE if he can adjust in SL till ALJN (as i was aware it will overtake Lalquila).