My experience is most S pen are interchangeable.
Note2, 3, 4, 5, Tab A are all interchangeable.
They may have difference in pressure level (but at least 1024), and the side button should work too.
My experience is those retailers probably don't have the knowledge/experience to answer this question.
Your best solution is to use the Note 4 pen on the tablet and see if it works.
S Pen will not work as there's no WACOM digitizer layer built into the hardware, only those version specifically mentioned with S Pen has those embedded into the tablet, and price should be higher too.