For whatever reason, lifetime points are not showing correctly on the Marriott website. They are aware of the issue and are working to fix it. My lifetime points were correct as of July 31, 2014, but haven't changed since. When I talked to customer service, they had the correct balance even though the website is wrong.
You might want to check out this thread Lifetime points are not up to date and several others like it.
If you're really concerned call to get the correct total.
100% right on that fastpofm, both criteria are required to meet the lifetime thresholds...
LT silver requires 250 nights and 1.2mill poinys earned;
LT gold is 500 nights and 1.6mill points earned;
LT plat is 750 nights and 2mill points
AS you've stayed 833 nights, the only thing you need to know is your lifetime points total... below 1.2 mill points and you're working hard, but hardly working!, 1.2mill-1.59 mill is Silver, 1.6mill-1.99mill is Gold and over 2mill and you're Plat. Call and they'll tell you which!
As a matter of fact I am now at 499 nights and 1.66mill points, so when I checkin to the Philly Marriott on Thursday 30th October I'll be qualifying for LTgold, actually, I will technically get to LT gold on Halloween...