Code gestion 70 is merely the code to show that you are within the group covered by “Conventions internationales (CEE et conventions bilatérales)”. The same way the ‘99’ in your social security number shows you are born outside France.
Our attestations run as normal for 12 months, and I am really not going to fret myself about this.
If the UK reneges on the withdrawal agreement then we will rejoin PUMA as we did previously. It is open to all french residents, and for those on low incomes it is a modest cost. And someone who has just the UK state pension probably won’t have to pay at all. It is 8% on your income above about 10,000€.