Interesting discussion friends and I admire all this knowledge.
Now here's my case: In my hands I have an original delivery note from Heuer Leonidas SA, Rue Veresius 18, Bielle, Switzerland ,dated 6.2.1975 It is an originally hand-typed price of paper.I received it with this watch 2 yrs ago. It carries the following text:

votre envoi du : 13.1.1975
Ref No: 1133N/11
Boite: 161816
Remis en etat: 1 chronographe, change de mouvement/ Service Garantie

Doesn't this mean that a Monaco 1133N ( case no. 161816) has had its calibre changed unter warranty early 1975? Wouldn't this mean that the watch was most likely built after 1971 ( warranty case) The 1133N code was clarified to me my Jean Jacques Racine, Heuer's Chief Watchmaker in the old days who confirmed during our visit past May 2008 that the Monaco with all-grey dial ( so no subdials with different shade of grey) was internally called 1133N at Heuer.Or aren't non-1133B Monacos not part of this analysis. Greetings!!! Ron