It took me to here by following the path to information on residency;
That is the link given for the French Interior Ministry’s site.
I am not affected by the CdS situation but have tried to get a grasp on it as my wife has dual nationality and if we decide to return to France we would be be able to use her U.K. one if that route remains particularly straightforward.
I know that U.K. Citizens do not need a CdS. I also know that Brexit is probably likely going to happen within weeks and that the British Embassy in Paris has recommended that Brits get prepared for the future. The advice has always been to apply for a CdS -EU EAA and Suisse but the current advice is to change tack and to go through the IM’s site. These details have been shared on this forum and others for many weeks. The IM portal is specifically designed with a no-deal Brexit in mind but I’m sure that they will adapt it if a deal goes through, the final card may be different but the process will not change very much.
As I said I found your post mid-timed and confusing. I still do. In your latest post you are confused about the term CdS, that’s not rare as the card already issued to UK citizens is entitled Titre de Sejour but later uses the term Carte de Sejour. (this too has been discussed to death) No new card has been invented for British applicants although the process of application has been simplified. With a no deal the CdS/TdS needed will cost €119 (instead of the usual €269) but in the case of a deal it will be free. Do you know how the fees are calculated? I do!
I can see no indication that the OP is applying through the old system, in fact I had presumed that they would be following the more recent advice. Both application systems ask for the date you entered France. For me that’s normal, making the most of the time we’re allowed in Europe has been a balancing act and the time and date of arrival and departure has been critical.