Understanding Equivalent Wyckoff positions
It seems to me that care has to be taken with the words 'equivalent'  and 'same' in the definitions above. Equivalent positions do not mean the same position. In the case, say, of a 4 fold axis any point say in the first quadrant can be replicated to the other three quadrants and these are equivalent points but not the same point, clearly. In some cases such as with reflections in a plane, two sets of identical (or equivalent) points may be produced and so and the number of equivalent points is reduced. The number of equivalent sets is called the multiplicity. These have been called special positions when they lie on a symmetry element 

In the Wycoff notation equivalent positions are labelled consecutively $a, b, c\cdots$ starting with $a$ for the highest symmetry. A position 2f, for example, indicates two equivalent atoms at position given by symmetry f. For each space group a table of general and special positions can be made.  This includes point symmetries, positions multiplicities and Wycoff symbols. The table below shows examples.


Table copied from  page 75 of 'Introduction to Crystallography' by  D. Sands, publ. Dover