I was just guessing as to what was going on with that dope. There is no way for me to know, and I never meant my answer to be taken as being THE answer.
I don't know how to explain this phenomena. The fact is, #3 and #4 are different. One cannot be shot without being altered, and the other cannot be smoked without being altered. The asshole thing to say would be one of you has a very powerful placebo going on, but that can't be the case, because placebo may work once or twice, but eventually you know what's going on.
An alternate explanation is that somehow you managed to add enough heat to the un-caffeinated heroin so that it vaporized but didn't burn. The reason you are supposed to add caffeine to #4 is because it lowers the melting point, meaning it will vaporize before it burns off. Without caffeine, it should be almost impossible to do.
However, the addition of other cuts could give you the same results as adding caffeine. Depending on what cuts they were, they could have lowered the melting point. This would actually be the most likely explanation, because the cuts wouldn't always have to be the same. Different proportions of different cuts could all theoretically achieve the same results. But really, what are the odds that all these different dealers just happened to add the exact amount of their preferred cuts to make the dope smokable? Slim to none, my friend, slim to none.
In other words, there is no way to know for sure what happened. You were able to smoke it and your friend was able to shoot it. Just be happy with that, I guess. There's nothing else we can do.