I can't remember ever seeing flowers on my potted tridents (except the Taiwan variety) - 30 years or more. Regularly get flowers on JM in pots.
Tridents in our garden produce loads of seed after 5 years or so here. Now we have a problem with trident seedlings all over the garden and in all the pots in the nursery. Hundreds of thousands of them germinate in any mulched garden bed and are tough enough to survive our summer even without water. No longer need to collect seed and germinate to get trident stock to work with.