NFL offseason training activities give the NFL world the first glimpse into the coming regular season. Rookies mix with stalwart veterans and free-agent signees, and new coaches get their bearings and install their systems.
Depth charts, position battles and possible alignment changes get their first exposure to the outside world. Sometimes there are surprises, and sometimes there aren't.
Either way, the outside world only gets a peek. The general public sees nothing, and even the local beat writers and media only get limited viewing windows. From those tidbits, information-hungry fans and media alike extrapolate as much as they can about where teams and players will be at headed into training camp.
Of course, this leaves a lot of huge questions unanswered, or only partially answered. We still don't know a lot of very important things about some of these teams, even after the first wave of OTAs.