I do know that they need at least two plants to fruit.
The year I grew them, it appeared that one was "female" and most of the little "balloons" would swell and turn to fruit. The other seemed to be "male". It was covered in blooms which turned into smaller "ballons", but most didn't swell or develop into fruit.
The "male" did have a few fruit later in the season, but only a handful.
If may be that three of yours are non fruit bearing (or late fruit bearing) and only one is going to be "female" and bear a lot of fruit. I don't have any clue why they become one way or the other.
Fortunately, even one plant will give you a nice amount of fruit.
