I have Jetpack. Among other things, it gives you a graph of your daily visitor count.
I once invested in buying visitors. The visitors did not show up on Jetpack. I complained to the vendor. I did not tell them about Jetpack. They assumed I had Google Analytics. I don't know Google Analytics.
Their explanation was Google Analytics was not accurate and only records less than 10% of the visitors. If that was true, then that was true also for Jetpack and perhaps other systems.
The vendor might have been accurate. One of my affiliates gives me totals of impressions and I was getting the impressions, but not the visitor count.
Does anyone else wonder about this or have encountered this and wonder if it is true? I have not yet applied for Google Adsense. I want to have a decent visitor count before I do.