hi,
I asked myself the same thing when I changed there.
there were 2 objects/ways ID:205729455 and ID:100497100 for Farakka Barrage. I didn't change it because I wasn't sure why, too.
dam ID 100497100 was created by PlaneMad changeset #7334148 13 years ago, dam with ID 205729455 was created by Japa 11 years ag (changeset  #15048310) 
regards