I found an issue with the 1.5.0 edge API where the getLabelPosition will return 0 if it doesn't find the label name. This is the current description for the function.
Description: Returns the position of the label aLabel in the default timeline, or undefined if aLabel is not a label on the timeline. Behavior is not guaranteed if aLabel is not a string.
Since it doesn't return undefined, it makes it impossible to have logic that tests for symbols that don't contain the label. Currently, the only work around I can think of for this is to modify the minified source directly.
Flynn