Synology NAS: going from 3856 bad sector count to 0

I've received my monthly dick health report like this:

Dear user,

The following is your monthly report regarding the health of disks on DiskStation. You can also check the health of individual disks at Storage Manager > HDD/SSD > Health Info.

Disk 1: Disk Recoection Count 2 Bad Sector Count 3856 Disk Re-identification Count 0

Disk 2: Disk Recoection Count 0 Bad Sector Count 0 Disk Re-identification Count 0

Sincerely, Synology DiskStation

Since then I've made a task schedule every week.

Now I get:

Disk 1: Disk Recoection Count 0 Bad Sector Count 0 Disk Re-identification Count 0

Disk 2: Disk Recoection Count 0 Bad Sector Count 0 Disk Re-identification Count 0

How is that possible ?

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