My question is this:
Let's say their are no checkpoints , rolling or coded.
Someone buy the old private keys or at some point just actually owned over 51% of a coin total.
Say they try your attempt , but it was 3 months earlier when they owned coins.
The Blockchain has 3 months of confirmations ahead of them at a rated say 1 minute interval.
How do they ever catch up , with the block height of the main chain, won't they always be ~3 months behind?
* Now if you say it is possible to trick the time setting and somehow condense those 3 months into a day, please provide details or proof on how that is done.*
Because block production has zero cost, and there is no way to objectively verify any given block as being created at time T.
Cost is not the issue, Each Block has a defined target of say 1 minute between blocks.
Your chain is 3 months behind, and still has a target time of 1 minute, your block height will always be ~ the same 3 months behind and as such never a threat to causing a reorg, because a reorg can only happen if your block height # exceeds the main chain.
So how do you make up the 3 months time difference?
FYI:
Any change to the code to modify the time target between blocks could allow faster blocks, would lower the target difficulty making it a weaker chain and also break consensus with the other nodes, therefore making sure it would never be accepted over the main chain.
FYI2:
The phrase
(block production has zero cost) , is incorrect.
There actually is a cost , it is time.
Your block has to wait the coded time before block generation can occur, and those coins go dormant for a coded period, another time factor.
The Time between blocks is hard coded which affects the difficulty # in proof of stake coins, thus defining the strength or weakness of a chain.