If that's all the vitamin instructions they gave you, you would be in trouble. With gastric bypass there is also malabsorption of B12 (and possibly of other B vitamins as well). B12 deficiency causes peripheral neuropathy, and I have seen threads on that other website where one person discusses their problems with peripheral neuropathy and a bunch of others chime in with their problems. And if left untreated, it can become permanent and disabling.
And the calcium, for both bypass and DS, should be calcium citrate, not the more common calcium carbonate.
People with both operations can have issues with iron, probably more with bypass than with DS but we see this with either operation. So you can't avoid supplementation for either calcium or iron.
With the DS, since we absorb so little fat, we also have to supplement the fat soluble vitamins - A, D, and K. E is also fat soluble but it's rare to have problems with E. And taking ADEK's won't work. They sound perfect, but in reality contain so little of each component as to be useless. So we take them separately in the "dry" form because if you take the prescription form, or the standard OTC ones, they are packaged in oil, and oil=fat so we don't absorb them.
There is a lot to know, and sadly most surgeons and their staff fail to provide adequate information. And then, they slam the DS for causing deficiencies, when in reality it's their crappy recommendations that caused the problem and not the operation.