If they are fudging the numbers to make the picture better than it is, how come, year-after-year they reveal the number of memorial partakers is increasing? That surely is as big an embarrassment as any decrease in numbers on other variables such as average publishers and baptisms.
My take on it is that it's a little easier to fudge the publisher count numbers than the partakers, while still being able to explain it away to the believers that are involved in compiling the numbers. They don't have an official policy on it, but from what I've read here from elders and such it seems to be unofficially the case that elders get a good reaming from the CO if they get a new irregular/inactive publisher, so they hound everyone to submit time and if they don't have any they're asked things like "well surely you've had a few spiritual conversations at work that added up to an hour?" and people will usually just let 'em have it. So you get publishers that aren't doing anything but report time nonetheless. Then obviously there are those that don't want to be hounded at all, and knowingly report false time to stay off the radar.
Additionally, there's the issue with the "peak publishers" number that they essentially just count the number of timeslips that they get each month instead of what would be trivially easy (these days) to actually tally them by month according to what month the timeslip is for. Also, I wouldn't be surprised if they counted peak publishers individually in each country/branch/whatever and added them all up to get the reported peak (i.e. one country's peak might be from april while another's would be from july). This would significantly distort the figures, but to the simpleton JWs doing the stats it would seem harmless.
Also there's the issue of 3rd world growth making up for the loss in developed countries. They've clearly tried to disguise this, though, by combining branches and then reporting the total for the new (larger) branch and comparing it to the previous (smaller) branch. I think they recently did this by including some new territories in with the US branch to hide the decline or make the growth look better than it really was. Of course they don't mention this combining when they publish the numbers.
When it comes to the number partaking, though, it's a little more cut-and-dry. They already tell elders not to count "worldly" people who are just treating it like communion, and I think they usually talk to others before counting them if they partake. That's about all they can do. Once the numbers make it up to the branch, there's a lot less that they can do to spin them and be able to rationalize it away.
I wouldn't be surprised if they dropped the count of those partaking altogether very soon, though. And maybe they'll quietly push out a QFR article about it.