Need Help Identifying Time of Old Map

[Haviland]

This may not be the right site/forum for this question; if you know of another forum I might post this question, please let me know.

Not being a cartographer, and not being educated in the study of ancient maps, I'm trying to identify the time that this map of Normandy was created:



(Or you can take a look at he map on my server:
http://havilands.org/1792map-300dpi.jpg )

The map image is courtesy co-researcher Robert P. Haviland.

On the lower right it appears to say "an.1792" which would indicate the year 1792. But a counter-argument is that it says an A 792, wherein the third A is capitalized and faded, and the year of the map is 792. I don't know enough about ancient maps and cartographic legends to understand the validity of these ideas.

I have a second question about this map, which is the basis for asking the question about the map's date. At the top, in the area that used to be Neustria before the Norman invasion, in the Cotentin Peninsula, there is what appears to be a double-shoreline and the symbol of a triple-turreted fortress:



I think it reads "Pt. Abilant." This is significant because the Haviland (de Havilland) family is said to originate in Neustria, on the Cotentin, from a fortress called Abilant, "three flights of an arrow" from the mouth of the river Saire, which is pretty much where this label indicates. Also, the Haviland / de Havilland coats of arms feature a tower triple-towered almost exactly like the symbol on this map (which is a charge shared with the kingdom of Castille and a few others, but with different colors).

But the area indicated on this map appears to be out in what is now the ocean. We have studied more modern maps of Point de Saire, and the shoreline has certainly moved inland since the first century. So the question is: is the old map trying to indicate an older shoreline, or a shoreline at low tide?

The castle was sacked by the Vikings in 888 or thereabouts, so it was standing in 792 but it was gone by 1792. The family would settle as "de Haveilland" on Guernsey by the 1400's, and at that time I don't believe there was any longer a castle Abilant standing on the Cotentin.

Any thoughts, including further expert insight on this old map, would be appreciated!