So I'm going to just copy and paste the TDA rules here as they are one of the most common set of rules enforced around the world, and often if a place is not using the official TDA rules, they're using a variant of it or something that was built off of it. In any case you should check with your local casino what they're doing as different places can have different rules, they will be somewhat similar to the below. I also added an explanation of some dealer terms you might not be familiar with from the TDA rules. TDA rules can be viewed here.
A: Misdeals include but are not necessarily limited to: 1) 2 or more boxed cards (boxed card is when a card is faceup in a deck of
shuffled cards) on the initial deal; 2) first card dealt to the wrong
seat; 3) cards dealt to a seat not entitled to a hand; 4) a seat
entitled to a hand is dealt out; 5) In stud, if any player’s first 2
downcards are exposed by dealer error; 6) In flop games, if 1 of the
first 2 cards dealt off the deck or any other 2 downcards are exposed
by dealer error. House standards apply for draw games (ex: lowball).
B: Players may be dealt 2 consecutive cards on the button (see also Rule 37).
C: In a misdeal, the re-deal is an exact re-play: the button does not move, no new players are seated, and limits stay the same.
Cards are dealt to players on penalty or not at their seats for the
original deal (Rule 30), then their hands are killed. The original
deal and re-deal count as one hand for a player on penalty, not two.
D: Once substantial action occurs a misdeal cannot be declared; the hand must proceed (See Rule 36).
36: Substantial Action (SA)
Substantial Action is either A) any 2 actions in turn, at least one of
which puts chips in the pot (i.e. any 2 actions except 2 checks or 2
folds) or B) any combination of 3 actions in turn (check, bet, raise,
call, fold). Posted blinds do not count towards SA. See Rules 35-D &
So given the above let's use these rules on your situations you provided:
- This will be a misdeal if the first hole card of either the SB or BB is exposed, otherwise continue dealing and provide the player who had a hole card exposed a new card after all players have received their cards. I.E. Continue around as normal, all players should have 2 cards, player who had an exposed card will have one, give them their second card after everyone has their two cards.
- Under TDA rules no continue dealing, after both the SB and BB have their initial hole card. However you are correct many places apply this rule to the first four seats, other places will also apply this rule to everyone must have a single facedown hole card otherwise it's a misdeal.
- This is the normal done thing, to continue dealing, the exposed card becomes the burn and the original burn becomes the players hole card. Again places do different, so if in doubt ask a floor staff what the ruling is.