I'm trying to track down when the International radio prefix XT changed.

In the 1950 ARRL Handbook the prefix is assigned to "France and Colonies and Protectorates".

It changed towards the end of the decade to Burkina Faso.

I'm interested in what it was in 1951. 

My 1954 and 1955 handbooks don't have the same type of general table in them.

Thanks

Mark K3MSB