Currently the labels in the chart widgets have two problematic aspects:

1. They are used as UIDs but this must not hold true in all cases
2. Because the should be unique ther are automatically altered in the chart widget and the user has no control over the new/label or id. Therefore e.g. removing such a chart becomes very tideous.

We should over at least more control. So either the caller should be able to receive the altered label when adding a chart. Or (what I still deem better, had already a discussion with Tobi Stein once) we should not allow to add a new chart with the same ID.
In this context I also would introduce a ID and label, where label is optional and the human readable "name" of the chart in a plot legend. ID is used to identifiy the chart when interacting with the chart widget.