Original or copy? Tintoretto

There is a huge painting in the Shipley art gallery in Gateshead that is a Tintoretto. There is another in the Prado museum in Madrid and a third much smaller one in Canada. The painting is Christ washing the feet of the disciples. The painting originally hung in a church in Venice with the Last Supper opposite it, on the side walls of the church at the back. The main figure of Christ is at the extreme right of the painting because that is the part of the painting that would be closest to the congregation. It was the custom at the time ( the 1500's) to decorate churches this way and if a wealthy person liked the painting they would commission a copy for themselves. The question is- which was the copy and which the original. Note both large paintings have been confirmed to be by Tintoretto so there's no question of who painted them but the question is which came first. The Prada claim their's is the original from the church and so do Gateshead . I went to a talk about this at the gallery in Gateshead today. It was very interesting like a version of the UK TV programme Fake or fortune where experts present evidence about paintings being originals or fakes. The lady convinced us that our painting is an original. The Prada one has been heavily restored and ours hasn't so ours appears much darker.