Number of restore points

[HPersson]

Is there any documentation of when a restore point is created?

Sounds like a straightforward question with the answer, when you take a backup... But don't agree on that

For example, 1 job that runs last saturday every month, forward inc with active full twice a year and synthetic full enabled on sundays.
I want to save these for 1 year. Logically I would set the numer of restore points to 12, but the Active full counts as 2 additional points. Then the scary part, the Synthetic full runs every Sunday, even if there hasn't been any backups during that week. So now we are up to 52 more restore points for a total of 66.

So what are the rules for this?
If I run a synthetic full on the same day as a inc is taken, will it be 1 or 2 restore points?
Active full on the same day as a Forward Inc?
Active full on the same day as a Reverse Inc (think that counts as just 1 restore point)?

Can't be alone to have miscalculated the number of points, just to realize that I don't have the monthly backup that I need available anymore!

[foggy]

For example, 1 job that runs last saturday every month, forward inc with active full twice a year and synthetic full enabled on sundays.

If your intention is to have just monthly backups, there's no need to enable synthetic fulls for a monthly job with active fulls set to be performed twice a year. You can disable them and go "forever incremental" with periodic active fulls.

I want to save these for 1 year. Logically I would set the numer of restore points to 12, but the Active full counts as 2 additional points.

That's not true, actually. Active full starts the backup chain anew creating brand new full backup from scratch and is counted within the specified retention policy. However, with forward incrementals, the number of restore points on disk varies from month to month (in your case) and you will have 12-17 restore points depending on the current month.