I just came across this on https://brexit.gouv.fr/sites/brexit/accueil.htm
“Les personnes déjà titulaires d’une carte de séjour permanent ayant été délivrée en leur ancienne qualité de citoyen de l’UE bénéficieront de plein droit de l’échange de ce document contre une carte de séjour permanent « accord de retrait ».”
Google translate gives this.
"Persons already holding a permanent residence card that has been issued in their former capacity as EU citizens will automatically benefit from the exchange of this document for a permanent withdrawal card “withdrawal agreement”. "
It could have been more specific if it had used the phrase, "… holding a permanent residence card that had been issued in their former capacity as a citizen elsewhere in the EU " [My italics.] I have read it as such.
If this is the case it has answered a question I have put to this forum and others but without reply, "Does residency elsewhere in the EU count towards or have any bearing on obtaining residency in FR? "
If anyone can confirm or refute my reading of this I would be most grateful.