Only the 66 and 67 SMS sets come in the hard plastic holder. The 1965's came in the pliofilm packages.
Ripley, I hate to say it, but the Half Dollar in your 66 Special Mint Set looks like it is a business strike. The luster doesn't seem to go along with the other coins in the set. You had said that the set opens up easily, my guess is that someone did exactly that and switched out the Half Dollar for another (probably a business strike) in the set pictured. Just a gut reaction.
You really think you can identify one based on a picture when the foremost experts there are can't identify one in hand ?
no, I don't Doug, that would be ridiculous. But look at the pic. Look at the luster on the Half vs the rest of the coins. Like the old sesame street song, "one of these things is not like the other". It could be a bad reflection or angle, it could be a crappy looking Half, but you can't tell me that the Half looks like the rest of the coins in that pic. The luster is different. If the case is easily opened is it not possible that someone swapped out a really really nice Half for one that they had?
Mike the rest of the coins in the set are CuNi. Perhaps the difference in luster is that. Its hard to be dogmatic over SMS the mint containers do open easily and substitutions are very possible .