They would be the same thing, possibly in a different format. Generally wan = pills, pian = tablets, tang = tea. So the last part is speaking of the format - wan being the common small ball pills in prepared formulas sold in bottles, tang being the raw herbs in a tea, or possible from granules. What makes this slightly more complicated is wan and tang can also in a way just mean formula. So on our herbal formulas page for Gui Zhi Fu Ling Wan, we use wan as a general indicator, but it's just the formula page which could be prepared in pian, tang, wan depending on the practitioner.