The canon firmly establishes that ROTJ takes place one year after the events of TESB.
How?
Every bit of official information around says that in the Star Wars universe, TESB takes place 3 ABY (3 years after the Battle of Yavin), and ROTJ takes place 4 ABY.
Where does it say that in the films? And what is ABY, in which scene they mention such acronym? To me it always seemed pretty vague how much time had passed between each movie.