I'll put it to you the way I put it to ....:
You have a guy who gives out one story soon after the fact. 2-3 decades later, he starts telling a very different, more involved (and jucier) story about the same event. You know that the other witnesses to the same event told a story that was consistent with the guy's first story, but contradicts his later one. The question to you is, which of the guy's two stories do you choose as most likely to be correct?
Well, if you are used to jumping to conclusions, then of course you are right. Burroughs' later version does differ from his original one.
But there's also another way of looking at things. Life's experiences have taught me that where humans are involved things sometimes get very complicated very quickly. For one thing, it hardly ever happens that a witness to an event will instantly tell you the whole story of what they saw in a concise manner. They normally forget details, which they will remember (differently) later, or leave out things they consider not to be relevant, even though they may actually be extremely relevant. Time is also a factor, as people caught up in a stressful situation, when it happens, may well tell a different story, from their original one, when they had a possibility to take a step back and quietly process the information. Obviously, this doesn't mean that their memory improves with time and there will always be bad actors who purposely change their story, but to simply dismiss later recollections is not credible is once again the same as jumping to conclusions.
The mere fact that Burroughs later recalled things that Postal and/or Brewer never confirmed doesn't automatically mean that Burroughs' recollections are false. And even if his earlier statements are similar to those of Postal and/or Brewer (which is a judgment call by itself) that still doesn't mean that he told the entire story soon after the fact.