Uh dagger supporters, your whole theory rests on timing. That he had the dagger and is now lucky and he got lucky during that time and after. You guys seem to be forgetting that the series was set in that time and so of course the dagger period will coincide with all the stuff going on at that time which his luck could be attributed to. Here is why the dagger theory is wrong:
1.He was just becoming a ta'veren during the time he had the ring. Or the increase in luck can be any other number of things such as his importance for tarmon gaidon, possibly being a hero of the horn reborn etc.
2.You have not even been able to come close to giving any explanation of why his luck would grow stronger after losing the dagger. That pokes a huge whole in your entire theory. If it was caused by the dagger there is no reason why it would get stronger after the dagger is gone. And you can no longer cling to the timing thing since i have just shown that is idea is not solid at all.
Add these to all the reasons people posted earlier like how it is against the nature of shadar logoth, it causes rotting of flesh and isnt related to luck etc and you can concur that Mat's luck couldn't have been and was not caused by the Shadr Logoth dagger