Similar music albums with different GTIN

There have been observed instances of an album apparently released under multiple GTINs i.e. multiple albums with same cover and content but different GTINs. This is irregular since each album is requires by GTIN to have a single GTIN. Instances include:

• Otros Aires - Otros Aires
  • http://www.tango.info/07796095003394
  • http://www.tango.info/07798135080013
• Gotan project - La revancha del tango
  • http://www.tango.info/07798014098054
  • http://www.tango.info/03760038140112
    • Only reference is tango.info e.g. there is no corroboration by Amazon or Google. What is tango.info's source?
• Biagi Ortiz
  • http://www.tango.info/00724349536524 - believed released 1998-2002?
  • http://www.tango.info/00094637915820 - believed released 2006/2007