I'll try to answer these questions Meryl-chan
1)I'm not too sure which room are you exactly talking about, but I believe is the one that has some food stored on it...... well, what I'm going to tell you is actually a technique that ALMOST ALWAYS works...... just take down the other guards nearby, you can even do that without any rounds on your tranquilizer gun....... you just make them FREEZE! then do the usual thing, get their dog tag...... and then, just walk behind them (while pointing the gun, of course) and then unequip the gun without them noticing..... so you can just kill them giving them a choke hold, that way, you don't make any noise, and you don't waste any bullets
Now, that you have already taken down all of them, just leave for last that stubborn soldier..... and when he says "Are you going to shoot me?" or whatever just shoot in his arm as you already know, and as everybody else is dead already, no one will hear
2)Hmmm, that's so weird..... actually, I have all my dog tags in one single file.... I'll tell you how it worked for me: I just beated the game in normal for the first time, and only got the dog tag for Stillman because I had no idea about them
Next time, I beated the game, once again in normal..... but I beated it using "Tanker-Plant", not only "Plant" Now, when I did that, I got 100% in both. Then, I beated the game in "hard" (using again "tanker-Plant") but forgot to shake Olga when she was asleep
So I got 96% on hard in the Tanker, and 100% in the Plant. Then, I just played with "Tanker" to get Olga's dog tag, and got 100%
So, if you didn't get confused with all my ramble, you probably have noticed that no matter how I played it, or in which difficulty, or in which file I saved.... I still got saved all of the dog tags, so it should be working the same way for you........
Probably somebody else will need to answer this question to you!!!