I'd be interested to know the source...
I pulled raw numbers from the Council Membership Tool on my.scouting. See attached for today's report on 092, Atlanta Area Council, which @Jameson76 had asked for.
So, over five days, the current numbers changed to 15341, up from 15315 last Friday (+26). You'll notice the Dec 2024 number does not change (nor should it).
The number this will be on 31 Dec, as @Eagle94-A1 points out, will be the one to watch for to give the most accurate "real time" number for comparison. Although, I suppose if a Registrar has a backlog of applications or renewals, they can tweak the Dec 2025 numbers into Jan 2026.
I do not know about today, but I know about back in the day. The #1 membership stat was the December 31st number. That was the one used in reports, media, etc. It is also the reason why a lot of councils had recharter December; delinquent units are still on the rolls until February or March. Rational was that paperwork was a pain, and it can take that long to get things fixed.
The #2 stat was the June 30th number. That was used to set goals, see how much work will need to be done in Round Up, etc.
Finally you had a monthly stat, and that compared to the previous years monthly stat.
That is why you can see different numbers supposedly covering the same thing. While some will say it is "apples to apples," It is more like Granny Smith Apples to Gala Apples to Red Delicious Apples.
Trust me there is a lot of indignation. One unit now refuses to have anything to do with the council except paperwork: no camporees, no using camp, no purchasing supplies, no FOS, nothing at at. Most of the units do not use the local summer camp because the program sucks: it is a MB giveaway. Last time I went, inadequate supplies, equipment breaking, large Scout to Instructor ratios (30 people in Lifesaving MB; 15 minutes max on the water each day because you don't have enough canoes?!?!?!), and no improvements from complaints.
Families are seeing all this and no longer want to support the council. There is actually discussion about the county leaving the current council, and joining a neighboring one.