It depends on how long it takes the partner airline to post the points through and on how long before you return. If the points have posted, they can always look you up at the lounge reception desk.
The trick with moving up a tier is making sure they don't steal all your points off you!
Let's say that by the time you get to LAX on the outbound you have 495 points. That next flight gets you 280, but you hit a threshold so your status points balance returns to zero, not 275. A friendly call to diamond club should get them to credit the extra 275 points (it worked for me once), but as far as I'm aware it's discretionary and they're within the rules not to let you have them.