The easiest part of your question to answer would be the changes in his story as to what he did on Monday afternoon when he discovered DR *missing*. As stated by AZGrandma on the DP show, first he said he contacted D's friend T by the Lake, then he said T wasn't home, in another interview he said the first thing he did was go to the Marshall's office. Another time he says that he contacted D's friend R. I don't see this as "missing information", but inconsistencies.
Then there is the discrepancy of the time MR woke up and actually decided that it was unusual that DR was gone. First we hear 1:30, then we hear 2:30-3pm.
There are other inconsistencies that I'm sure others can more readily point out. These have been discussed in past threads here at WS, but I'm unsure if anyone has made a definitive list of what we have heard in so far as conflicting information about when it comes to things MR has said himself.
As for having it down by rote memory at this point - after 4 months of interviews, I would think it would be pretty clear and not changing. Perhaps not in specific words, but the order of events shouldn't change.
As always, all of the above is MOO, unless otherwise indicated! :cow: