What gives now?

In a conversation with my good coin dealer recently, he advised me to only buy slabbed coins and to have coins in my collection slabbed. I purchased another XF 40 platinum ruble from him recently. This is a three generation business that has been operating for over 40 years.So I took his advice and sent in four rubles purchased from him up to 18 years ago, before slabbing was a big deal. Each is supposed to be about a third ounce of platinum.What should have been fast turn around took over a month. And now I get the results back that the coins are of ?questionable authenticity.?It sounds like I am out of luck and might just as well pitch what were prized coins. I have asked NGC for further information. Anybody have any experience with this? Thoughts and ideas? This seems to be the ultimate ?body bag.?