I am trying to log what letters have already been used as a datum, so I can re-label some drawing views around it. While I have the re-labeling function working properly, I can't find anything on line that gets the already used letters of datums.
I think you would have to loop thorough all the drawing's annotations and check for a datum tag (see swAnnotationType_e) with IAnnotation.GetType. Then use IAnnotation.GetSpecificAnnotation to get the IDatumTag interface. Then you can use IDatumTag.GetLabel to get the letter. Keep track of all the letters used or create a function that always returns the higher of two letters (in alphabetical order) so you always have the latest letter used.