PoS does produce a reliable monotonic sequence, it's just that it doesn't go back to genesis. Every few months you need a checkpoint hash. The idea here is that

PoS does produce a reliable monotonic sequence, it's just that it doesn't go back to genesis. Every few months you need a checkpoint hash. The idea here is that this is rare enough so it's easy to find the accepted checkpoint out of band, like we pretty much do for client software already.