MASP rewards are lost to undated assets in certain situations

[murisi]

MASP rewards for a token are distributed equally amongst whatever amount of that token is locked in the shielded pool regardless of whether it is dated (AssetData::epoch == Some(...)) or not (AssetData::epoch == None). And to back these rewards, a sufficient amount of the native token is also minted in parallel. This state of affairs is problematic because rewards cannot actually be claimed for undated assets (because the system cannot determine how long such assets have been locked). So the end result in certain situations is that a proportion of newly minted NAM is unclaimable. One example of such a situation is a token address being added to the rewards program after users have already shielded/locked (necessarily undated) instances of that token in the pool.