When the production series of locomotives were ordered they incorporated what SNCB had learned from the 5 prototypes.

The five prototypes were rebuilt in 1976-1977 to bring them up to standard with the production batch, which had a number of small improvements.

Unusually for SNCB, the French heritage of these locomotives got them classified as B′B′ rather than Bo′Bo′, being fitted with licence-built Schneider monomotor bogies.

SNCB decided to stop replacing them to avoid the large amount of extra time and labor involved in a normally simple task.

Another negative point was this small class had almost no commonality of spares with earlier versions.

All ended up blue when SNCB decided that yellow locomotives needed to be washed more often than dark ones, a lesson since forgotten given the livery of Classes 13, 18², 19², AM96, AR41 and M6 and updated M5 coaching stock.

The reason was to put more seats on the busy line from Ottignies to Brussels during the peak commuting hours.