Good comments Talbot. And to add a fourth. GPS can aslo be out. Accuracy of GPS can be out as much as 30-40m(100ft'ish). This can be for several reasons. Poor signal aqusition due to atmospheric conditions such as Rain, objects in line with antennea and satallite/s such as a sail and especially if sail is wet, satallite malfunction
, not enough satallites being recieved. It takes a minimum of three for a position, but the more satallites recieved above three, the more accurate the position becomes. And of course the good ole military taking the whole set up "out of focus" so to say, for security
However Jon, for one chart to read different to another, I would be looking at your system setup. I don't know your programme, but you should have the ability to enter an exact Lat/Long correction figure somewhere, so as to align the chart to the GPS. Of course, you need to know of a physical place, the Long/lat for that point and you need to place your boat there.
And it may be as others have said, the fact that the charts are just incorrect. That's why they have warnings on the Echarts that they should not be relied upon as sole navagational aid.