Hi, Kirk. ESRI shapefiles do not contain any topological or label information. The data associated with each shape is stored as a table of records in an additional file (in dBase format - *.dbf). The software that shows ESRI shapefiles then uses this table of records to extract some textual information for each shape and create labels, fillings, strokes, etc. As only textual information is available in the DBF file, there's no way for the software to know where to place the label. That's why Nevron Diagram uses a sophisticated label placing algorithm to determine where to place shape labels.
If you have placed a label manually in your third party software package, this means that either it has stored the label placement information either in an additional file (not part of the ESRI shapefiles) or it has created a new data column in the DBF file to store label data. In the latter case you will be able to access this information when importing the shapefile in Nevron Diagram and using it you will be able to manually place the label based on this information. But you should know in advance how this data is stored and how it should be interpreted, because as I've said - by specification there's no way to store label placement data in an ESRI shapefile, so there's no standard way to read such data.
Best Regards,
Nevron Support Team