Not necessarily, what is the name of this one - is it a early summer bloomer - is it a small or large flowered variety ?
Pruning and flowering periods rule clematis and if you get it wrong you'll forfeit your flowers.

You've done well to keep it so healthy and prolific considering you restrict it by potting, they have long roots that require extremely deep runs.

We do need to know the variety as some are now bred specifically for use in pots, being smaller growers, and some are herbaceous types (i.e they die right down each year). That info will help towards the correct pruning/cultivation regime

Thanks, both! The clematis started flowering about 4 weeks ago and is still flowering. The spent flowers are turning into, what I think of as, typical clematis seedheads. Unfortunately, (& untypically) I've lost the tag it came with & can't remember the name but it is a variety that's suitable for growing in pots and the flowers are sort of 'mid-sized' and purplish - very pretty growing up a small obelisk at my front door!