Yes,i am aware of the differences between the drugs. In the above mentioned case,giving the vitamins along with Corid,is why chickens did not respond to treatment. I always caution on the use of vitamins for this very reason.There have been studies that show a vitamin supplement can be given with the Sulmet or Di-Methox as they are not true folate blockers. Similar, but not quite. I would do this on a bird to bird case. If I had a bird that was totally wrung out from the cocci, then yes I would give an vitamin along with the sulpha drug. In the case of a bird showing the normal symptoms of resistant cocci, was not at death's door, then you are right and they shouldn't be given the vitamins and risk having them not work completely.
I did have to make this decision last year with mine and did give vitamins to 4 birds that had no chance without them. 1 died from the cocci on day one of the treatment, but the rest healed and are still alive. I used the 4 day treatment with the Sulmet at that time.
I try and make my answers as simple and precise as possible,so that there is no misunderstanding or confusion about directions on drug use. If i were to say,you can use vitamins with Sulfonamide drugs(sulfamethazine-Sulmet/sulfadimethoxine-Di-Methox),my concern is that there would be confusion and the result would be chickens not responding to treatment and dying.