@Duckiedoggo
We've seen Paris, Marseille, and other big cities in the last few chapters. There's no way that Sedan and Dijon are the only safe places in Gallia. The first chapter even mentions that the 506th was formed after the liberation of Gallia, and whether that means the start of the manga/LN or the foundation ceremony this chapter it doesn't add up.
It is my opinion that Noble Witches got the timeline wrong and it wasn't a retcon of any sort. The first Noble Witches Novel came out in 2015, but in 2016 Brave witches confirms the timeline as previously established with Gallia being liberated in late 1944.
Edit: Digging through my copy of the LN it seems like the manga simply printed the year wrong. The Volume 3 "intermission" before Chapter 3 sets the year as 1945, and later on during the Keera chase it sets the month and day as March 22. Anyways, thanks again to you folks for TLing another small piece of the Witching World. Can't wait for the Pantaloni Rossi!