If they're taken from active accounts, they're not really secure for over two months, if even that now. Basically once the original owner's ticket gets noticed and you still have your stuff, then it should be fine. But I would definately not send it to your main account for a very long time.
Also the method that works the best for me is shop sniping (Account where you hold the item puts the item at 1NP and account main buys it), make sure to use proxies when manipulating accounts so TNT doesn't -or makes less aparent- the connection between accounts
Seems like its worth a shot i have about 200M NP Pure/items wrapped up in shells i used proxies/VPN's Hopefuly but i have done a school boy error by putting some stuff onto my main thanks for your answer.