The Monza serial started around the 336xxx, are there any earlier ones out there, please have a look...
Interesting is that the Modena used the same ref number than the Monza, which could let us guessing that these have not been in the markets for the same time, Modena numbers are in the 360xxx hence this is a good indication that Modena was following Monza after the end of the limited series as proclaimed in the original Monza leaflet 1976.
Now also pretty new knowledge is that the Monza was also available with Monza printing on the dial in the cal 12 version, followed by a Modena cal 12 model for the German market, at least the Modena modelname appeared only once in a German catalog and was never advertised in the US.
Could you please have a look at your vintage Heuer catalogs if there is more info hidden somewhere ?

Cheers

Arno

www.heuerchronographs.com

: Arno (and other readers):

: Some time ago, Arno posted the follwing timeline re the Monza and
: Modena:
: Monza Cal 15 lauched MY 75/76 to commemorate F1 victory by
: NL, supplied in the helmet box and limited edition (Monza
: leaflet text) Monza Cal 15 add campaign dated 1976: Heuer
: verschenkt den Weltmeister, Monza center piece and cavalino
: helmet NL Monza Cal 15 Cat int 77/78 Modena Cal 15 Cat D 77/78
: Monza Cal 12/ Cal 15 Cat int 78/79, shown Cal 15 only, Mark
: please confirm which catalog you have seen the Monza cal 12
: pictured Modena Cal 12 succeding Monza Cal 12 for Europe..?
: Catalog 79/80 does not show Monza, Modena or eco version.
: 1980/81 launch of eco version.
: So now I am wondering: Do we have any new items or details to add
: to this timeline? Have we gathered any Modena serial numbers,
: and seen how they flow with the Monza serial numbers? Are we all
: happy with the story that the Modena was introduced after the
: Monza? Do we believe that the Modena was only sold in the German
: (or other European) market?

: Jeff