OK, it is hard to describe, but you might want to compare old patina with "new patina", be it on a nakago or tsuba. True patina is like porn, tough to define, but you recognise it when you see it.
Try to compare your sword's nakago with that of a good sword. Spot the difference.
You need to see some good swords, with good nakago. Good nakago has yasurime, even if it is quite old. Yours does not and there is a reason for this...
BTW, the nakago should not smell at all.
Another hint: think how much you have paid for it. I dare say it was not exactly expensive. Think of the possible reasons why:
1. The sword is pretty average
2. The sword is saiha
3. The nakago has been repatinated for whatever reason
4. The sword is tired
5. The sword is otherwise flawed
Just trying to tell you that buying nihonto is not that easy. One of my first swords had a hagire, thank goodness I have managed to spot it and return the sword.
Another one I gave stupidly to a "polisher" who ruined it by polishing it down and who produced a fake hamon. It still hurts, but I had no NMB back then.