I wasn't saying they aren't reliable. I'm merely saying that it is an estimate. I follow BOM frequently and post on their forums. They do not have the actual theater count until the Thursday before an opening Friday. Go take a look at this week's theater count for Friday openers:
Take a look at the part where it says "updated Thursday afternoons." We will not find out IM2's actual theater count until next Thursday. The 4,000 number is just an estimate, a conservative one. They underestimated TDK's theater count by a few hundred if I remember right.