Espalion said that Pierre Plantard was the first to use the term "line of 17th January," - which he referred to in 1978 where he wrote the preface to the new edition of "The True Celtic Language" by Boudet. He also defined the "line of 17th January" as "the line of
27° Capricorn." Plantard illustrates this by way of a diagram, in which he suggested that the line originates at the tower of Rennes-le-Château church, goes south to Rennes-les-Bains, and then crosses the Source du Cercle and its famous stone seat known as the "Devil's Armchair".
Epsalion then refers to the second line of 17th January, published in 1989 by Thomas Plantard, Pierre's son - (although the diagram is dated to 1973 and signed by one Antoine du Rocher). Epsalion says; "It [the line] connects the tower / cemetery of Rennes-le-Château with the church steeple of Rennes-les-Bains. This new line of 17 January no longer goes through the Source du Cercle and is designated by the "bell tower" on the first image'.
There is however another diagram which mention's the line of 17th January. In fact, it appears to mimic information on the Thomas Plantard map. But it was designed by Cherisey, with a date on the map of 1961.
The map comes as part of a Priory document called L'Or de Rennes Pour Un Napoléon (Bibliothèque Nationale, Tolbiac - Rez-de-jardin - magasin 4 - LB44-2360). It was deposited in 1975.