blocks can be "valid" but if they aren't the first valid block you receive, they don't get added to your copy of the blockchain. 

joda

bitcoin

Proof of Late Work (PLW): addressing the problem of intermediaries in layer 2 

I'm either too smart or too dumb for this. the miner with a valid block which is not included in the chain is either not a valid block, or a temporary chain split that will be automatically resolved in the next 1-2 blocks. This is be design and there is nothing to discuss here;) 