Here are the tricks for dating Michelin maps accurately, for those interested in determining the age of a Michelin map.
To determine the date of a Michelin map, one must rely on the information on the map, and not on the information that one finds on the covers. Michelin sought to control costs by using obsolete covers (and spines) until the stock had expired, no matter if the information on the covers was no longer accurate. And so it happens that one finds maps without legenda: The legenda was moved from the front to the back cover around 1950, and there was still a stock of old back covers that they did not want to write off.
One will almost always find the date in the upper left corner of the map, under the page number. This date started to appear after 1923. Before that date, there was just a number between brackets, giving the edition number (1 to 7 for some).
From 1923 to 1935 the following coding is used, 2 numbers separated by a hyphen, for example 2325-411
- The two first digits represent the year, 1923.
- The two next digits represent the total printed (multiply by 1 000), 25 000.
- The first digit after the hyphen represents the edition : 4th edition.
- The last digits represent the month.
In 1935 and 36 the 2 groups are inverted, for example 111-3629, 1936.
= 1936, 29 000 printed, 11th edition.
In 1936 and 1937 and in some cases 1938, all editions mention the year explicitly. The revisions within a year are indicated by a number (2 to 4) added beneath the year. From 37 to 40, the year is preceded by "révisée en" ("revised"). From 40 to 44 this becomes "édition provisoire" (preliminary edition) but this is not systematically applied. Sometimes both texts occur.
From 1956 onwards, a small dot is added to the year to indicate minor revisions. These dots still exist today. (get your magnifying glasses! there are sometimes three such dots!). Finally since just before 1970 (depending on the numbers), a logical sequences is applied to mark the different editions. This chronology is still in use today. The year referred to often being different from the year of the "dépôt légal".