if the stock is shabby, you look for another and leave it alone, to someone else who likes doing crappy weapons. at least its what i would do and would be happy to have such an option.
Besides, how much can a dagger wear? 4kg ? Sounds like one stock. Also, the stock don't disapear magically in the process of shaping it into a dagger, You heat it and start smashing with a hammer till it has a right shape. In Japan, smiths also found out that the more layers the swords has, the better it is. So, they were smashing they reshaped stock, then compact like a piece of paper and reshaping it again. If there is metal loss in the process, someone would have to find reliable source to prove it was so huge, because logically thinking it can't be big.