Answer
When using the Append File command on a Cadastral XML file to map extended attributes to their counterparts in an existing parcel fabric, field names must exactly match their target counterparts, in both case and spelling. Do not confuse field aliases with the actual field names; only field names are considered.
Field names can be viewed in an ArcCatalog table properties dialog, in a layer properties dialog, or in an attribute table in ArcMap. However, in an attribute table in ArcMap, field aliases may be displayed instead of field names unless the ArcMap table option to show field aliases is reset.