The cordon variety will have one strong stem that continues upwards, yes some buds will try to grow from where the leaf stalk meets the main stem, which you should remove - but it should be obvious that it has a main stem.
Red Alert will grow bushy (obviously
) and final height is 18ins to 2 ft at the most, seen side by side with the cordon, you should easily tell the difference as they get a bit bigger.
That all seems a bit vague, I know, but it should be easy, to tell the difference as they put on a bit more growth.