Every team uses a chart. There is no one single chart. And each year the chart changes depending on the draft. A deeper draft would have different values than a draft with just a few good players at the top. Each team creates their own chart every single year. So every season there are 32 new charts, each and every one of them a little bit different than the other. Really it's kind of a VBD sheet with names removed. Every draft position has a value assigned to it instead of assigning those values to other players. If a team feels that there are 13 impact players in a draft, then their 13th pick is going to have a much higher value than the 14th pick. If another team actually thinks that there are 14 impact players, then their 14th pick with have a higher value than the other team and their dropoff will occur at spot 15.
Any chart that you find on the internet is merely an example of what a chart would look like. As far as I know, nobody had ever gotten a hold of a real chart and posted it. If they did, some team out there would be very very very upset.