Well I've been planning to let some steam out regarding this for a while now. I have seen a notion on recent years where collectors are starting to "go against" shinsa results (regardless of the organisation) and it often happens when the attribution is not favorable or what one thought it would be. I've actually thought of making a small ranting topic on defending the shinsa for a while but never got around to it until now. You often hear the common phrase shinsa panels are just human and people make mistakes but they are still experts whose opinion at least I hold at high value. Those experts have the ability to see minor details in the blade (or fittings) that regular collectors miss. I was reading Kantei explanation by Hinohara Dai of May issue of Token Bijutsu where he went bit off from kantei sword to ramble a bit how some experienced collector noticed the very minor detail in curvature of near identical swords from Kamakura and early Muromachi on display and that raised many questions from other collectors there at present.
This comes down to what he explains that professional appraisers and sword dealers handle many blades on a daily basis. I could personally add to this group even active collectors in Japan as there are so many opportunities for that in Japan. I think all that he wrote applies to tsuba and other stuff as well. The experts see and handle so great number of items that average collector do not come even close to that. Yes we have some great opportunities even in Europe and US but we cannot compete with Japan.
But then there are those cases where it is not clear at first glance if it is a Kamakura or an early Muromachi tachi. In such a case, one sometimes hears comments like “how can an expert not recognize at least the period immediately?” That is, an expert should at least know right away if he is handling a Kamakura or a Muromachi blade. Well, from my own experience and handling somewhere between 100,000 and 200,000 blades, I can confirm that these cases exist and that they are not rare at all. But here it is recommended to bo back from examining the jiba to the sugata, the first traditional kantei point, and after studying the shape again more closely, eventually return to the jigane and the hamon. Often, the initial gut feel was right but that feel should either be substantiated or dismissed to arrive at a well-founded opinion.
That above is a direct quote from that write up by Hinohara Dai. Even though he writes about kantei of swords I think we can apply it to tsuba and other stuff too. When someone has handled and studied like 100,000+ items I wouldn't easily challenge his/hers opinion about this stuff. The shinsa teams are professional experts for a reason and they have so much experience to back it up.
I've just heard lately people from many medias stating that NBTHK made wrong call or NTHK do not know what they see etc. Perhaps it is the collector who might not see everything? I remember a bit funny thing from some years back when I took my tachi to NBTHK Scandinavian meeting, after seeing the sword Jan-Erik Svanberg told me few details of a sword I had had for multiple years that I had missed before. That was the first time I personally experienced how quickly experienced collectors can notice minor details and I was bit mindblown. Another great experience was at Utrecht 1 minute kantei session this summer. While I was at the right tracks I was amazed how much details experienced people picked up in just one minute.
So to sum it up if you think experts have got it wrong be sure to have lots and lots of research to back your own opinion and try to understand the expert opinion too. And if you think you can outsmart Japanese dealers it's a good idea to think twice as their knowledge level is very high and they handle and study very large amount of swords.