How do you handle the following situations:
1. Entry in a game where cards are already in the discard tray.
don't generally do it. If you must, then add the already dealt cards to your "cards yet undealt" number when computing true count.
2. Situation where you miss cards during the game.
just keep the count as best you can, blow off the few you didn't count, and try not to let it rattle you.