I have never believed the oft-stated claim that the WT fudges their membership numbers. I have never doubted that they report the numbers that are received. The local counts of publishers, attendance at meetings and at conventions, is very diligently done so as to appear OCD. The reports of attendance and publishers that I see in the published reports are consistent with what I observe anecdotally. What they have done in recent years is lowering the bar so as to boost figures. A bible study being a 15 minute door conversation, people writing a letter for 15 minutes counts them as a publisher, etc. Now they just need to check a box; it can't get much lower than that.
Census figures, which tend to show more JWs than the WT does, indicates to me that there are lots of people who self-identify as JWs but do not report being publishers to the WT. The new box-checking may change that.
Money matters (above the Local KH level) are another animal. There is no transparency and I have a high degree of suspicion.