According to http://msdn.microsoft.com/en-us/library/ms867702.aspx we can do some small improvements for ASF / WMA tags:

• Distingiush between WM/OriginalReleaseTime and WM/OriginalReleaseYear
• Save encodersettings to WM/EncodingSettings
• Save website to WM/AuthorURL
• Support WM/PartOfSet possibly containing totaldiscs

Probably the same logic applied for totaldiscs could also be used for totaltracks, but the spec linked above is not clear about this so I left it out.

Code to support this is in https://github.com/phw/picard/tree/improved-wma-tags