In the merge tickets popup, it displays the ID, Subject, Email and Start Date.

 

Unless you look at the base ticket and look for the ID, you have no idea which is the ticket you want to keep and which are the tickets that will be merging to the kept ticket.

 

It would be helpful to add the time of the ticket either as a separate item in the list of tickets being merged or add the time next to the date.  This way it's easier to look to see which ticket was the first ticket received, which is usually the ticket kept and what the other tickets are merging to.