I don't know what the current definitive rule is that determines whether someone is viewed as an "active publisher" or not. I've seen comments suggesting that it is reporting a certain minimum number of hours per month which seems reasonable.
What is interesting is how they change the definition of what an active publisher is based on the context. Normally, you are never doing enough, however much you are doing, and too little or some missed reporting will get you a talking to.
But note how they class 'active' in one of the latest Body of Elders letters:
The secretary should check the Congregation’s Publisher Record (S-21) cards and count the number of active publishers in the file. (Active publishers are all those who have reported some field service time within the past six months.)
That seems fairly relaxed doesn't it? Pop a field service report entry in for an hour once every six months and you are an "active publisher"!
Wait a minute ... why is that definition so relaxed? Well, it's so the count is inflated to be as high as possible. Why? Because it's for the congregations to work out how much they should be donating to buy the next circuit overseer's car. Yes, they want the congregations to pass a resolution to send 3.00 GBP x number of active publishers so of course they want the definition of "active" to be as loose as possible.
Isn't it funny how the definition changes based on whether it includes you in the head-count for a contribution vs whether it is a judgement of whether you are doing enough for the religion?
You always need to be doing more ... but when it comes to putting a price on your head for a contribution, it seems the absolute bare minimum is plenty enough to get you included!