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 see 03760038140112
• Biagi Ortiz
  • http://www.tango.info/00724349536524 - believed released 1998-2002?
  • http://www.tango.info/00094637915820 - believed released 2006/2007