For any posts BEFORE page 81, any NXT/BTC account that has been used to submit buy-in more than once should be reviewed. If tied to multiple accounts, refund all transactions after the first and mark the user accounts of all the subsequent requests as ineligible.
No we don't apply a new law retrospectively since it will ruin NEM's reputation.
Not in my opinion. It is in your FAQ...
4. How could you prevent multiple buy-ins ?
In short - We can't. Multiple buy-in will be possible with multiple accounts. We also want you to have the ability to buy a NEM stake for your loved ones so they could all join the movement.
However accumulating many NEM stakes goes against NEM's principles of fairness and equality, therefore the development team reserves the right to refund you the money if an effort to unfairly accumulate NEM stakes is discovered.Think the NEM reputation is taking a pretty big hit on this already.
Not as applying new law retrospectively, imho.