[JB]How do you handle the following situations:
1. Entry in a game where cards are already in the discard tray.
[nd] don't generally do it. If you must, then add the already dealt cards to your "cards yet undealt" number when computing true count.
I agree with nicdun not to make a habit of this practice. Suppose you are at a six-deck game with two decks in the discard tray. The correct procedure is to mentally put those two decks at the end of the shoe for computing true count. However, what you have done, in effect, is to move the cut card up drastically at the same time - you now are going to play three of the six decks - horrible penetration. Read the books mentioned in my article above.
[JB]2. Situation where you miss cards during the game.
[nd] just keep the count as best you can, blow off the few you didn't count, and try not to let it rattle you.
I disagree here; one should be so well practiced that this doesn't happen, ever. Only something "mechanical" should cause one to miss cards: a light fixture falls from the ceiling onto the guy's hand next to yours, the heat ignites the cards, and they burn to a crisp before the dealer can flip them. Even then, one might have had a chance to spy the cards as they were being played and the count adjusted from memory.
We can also imply counts: if that burnt-up hand stayed against a ten it's fairly safe to assume a -1 for the hand, as he probably had something like a K,8 - A-9, - or 10,Q. Assuming a -2 would be even more conservative.
The point is that we shouldn't be playing with real dollars if we have still have trouble keeping track of the cards. We should practice until we can follow the cards effortlessly. Just my opinion.
Best of luck,
Pork