2) if change is not always made and blinds are 600/1200 and the bb has three 500 chips in front, how do you rule when the betting round is limped to the big blind, and then the big blind announces raise and tosses out 2000 more? Is the total bet now 3200 or is it 3500? I suspect making intentions clear would be part of the ruling decision.
The above is a scenario where the player makes a bet on top of chips not yet pulled in. In your example there is change due from the prior bet. In other examples we could make the prior-bet chips may not have change coming, or they may not be enough to cover calling an intervening raise.
So now the player drops an additional chip or chip(s) on top of the prior-bet chips. In your example he didn't pull any of the prior chips back. In other examples we could make, he might pull some back.
In your example he declares raise but not an amount. In other examples we could make he might not declare anything, just put out a chip or chips.
In your example he doesn't toss the lot of chips forward, he just drops the new 2000 on top of the prior bet chips. In other examples we could make, he bundles all the chips together and tosses the lot forward.
ALL of the above share in common that the player has "make a bet on top of chips not yet pulled in". This general issue is the subject of new TDA Rule 44:
44: Previous Bet Chips Not Pulled In. If a player faces a raise and has chips in front of him not yet pulled in from a prior bet, those chips (and any change due) may affect whether his betting response to the raise is a call or re-raise. Because several possibilities exist, players are encouraged to verbally declare their bet before putting out new chips on top of chips from a prior bet not yet pulled in.The 2013 TDA Summit had an open discussion of this general subject. There were at least 6 or 7 possible scenarios presented in the Summit Powerpoint: Player silently tosses out an overchip on top of prior bet, player silently pulls a part of prior bet back then tosses an overchip, player bundles chips together and tosses forward, player pulls a chip back then puts out two or more new chips silently.... and on and on...
What we found was that polling the over 150 attendees, there was fairly strong agreement as to how to rule in some of these situations, but a wide disparity in others... The TDA could have written up elaborate instructions for each of these 7 or 8 permutations. But even then would TDs, and especially dealers, keep all the possibilities in their mind? At the end of the day, the reality is that for the time being these will be ruled as the floorstaff sees fit at the time IF the player doesn't make his actions unmistakably clear by verbally declaring their total bet amount first.
In your example, I think almost universally this would be considered a bet of all chips (i.e. 3500 total). But in other possible cases the ruling would not be so consistent. Hence Rule 44: Player is advised to pre-verbalize his/her bet amount, otherwise as you say, it's players responsibility to make their intentions clear and if they don't this bet may not be interpreted as they intended, and it's their responsibility, not the floorstaff.