Following really doesn't answer your question, but might provide some insight into your site ... all sites are different!
Complicated thing ... backups ... Yes, 1000 is good! Finished.
I have seen 700, 800, 900 though that have also finished.
There's a table:
mdl_backup_controllers
+---------------+----------------+------+-----+------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------+----------------+------+-----+------------------+----------------+
| id | bigint(10) | NO | PRI | NULL | auto_increment |
| backupid | varchar(32) | NO | UNI | | |
| operation | varchar(20) | NO | | backup | |
| type | varchar(10) | NO | MUL | | |
| itemid | bigint(10) | NO | | NULL | |
| format | varchar(20) | NO | | | |
| interactive | smallint(4) | NO | | NULL | |
| purpose | smallint(4) | NO | | NULL | |
| userid | bigint(10) | NO | MUL | NULL | |
| status | smallint(4) | NO | | NULL | |
| execution | smallint(4) | NO | | NULL | |
| executiontime | bigint(10) | NO | | NULL | |
| checksum | varchar(32) | NO | | | |
| timecreated | bigint(10) | NO | | NULL | |
| timemodified | bigint(10) | NO | | NULL | |
| progress | decimal(15,14) | NO | | 0.00000000000000 | |
| controller | longtext | NO | | NULL | |
have a 3.11.x sandbox site with very few courses doing automated backups ... and in the table above 'status' always shows 1000.
Know that doesn't answer your question ... specifically ... but might have to do with 'plan' that's built ... what to backup. So if you backed up a large course but excluded all video links .. that would be one 'plan'. Did see one course change below because I had been in there to tinker with annotating assignments.
Here's a command line backup of one course:
php backup.php --courseid=8
== Performing backup... ==
instantiating backup controller d5ea95579a9f7d72f4f9df2631cfce43
setting controller status to 100
loading controller plan
setting controller status to 300
applying plan defaults
setting controller status to 400
setting file inclusion to
checking plan security
setting controller status to 500
setting controller status to 700
saving controller to db
calculating controller checksum 7d6dfc74c8e9e0a2503fb9e771a8277e
loading controller from db
setting file inclusion to 1
setting controller status to 800
saving controller to db
calculating controller checksum 066fd6e681623a810715fe441e311b00
loading controller from db
setting controller status to 1000
saving controller to db
Backup completed, the new file is listed in the backup area of the given course
You can see the numbers are contronller status - guess in 'plan' building' (what to backup). CLI uses backup defaults ... whatever those are set to.
So if you were looking for a clue for failed backups ... controller status may not help much ... but inspecting what is in a failed course backup in moodledata/temp/backup/hashdirectory/ compared to what you know is not there might.
'SoS', Ken