Last year, I grew a Shirley plant with two vigorous main leaders. I got 5 trusses on each. Then a new plant grew out the side and I got a further 3 trusses of good sized tomatoes from that.
Some tomatoes strains seem quite good at risk management – when they have secured the first wave of fruit to a good size, they reckon they can go for broke and have a second lot, since they will spread their seed at season’s end no matter what.