Missing Time Machine backups

TonyWells wrote:

I run Time Machine on my MacBook Air and periodically attach an external drive to create an offline backup.

I needed to recover a backup of a database I have been working on to check some historical data.

When I went into Time Machine I had local snapshots for today, yesterday and then the 15th March. Nothing in between.

So it appears that no snapshots were made after the 15th March, 02.32am, until yesterday. I've attached a screen shot of the local snapshots.

Can anyone explain why this happened and what I can do to stop it happening again.

Thanks.

https://discussions.apple.com/content/attachment/c2baef54-4fef-4b95-a3f8-ceaf5f177b27

Typically Local snapshots are saved for only 24 hours then moved if the external drive is connected or deleted as new local snapshots are produced.

Local snapshots are moved to the Time Machine disk when connected.

"Your Mac counts the space used by snapshots as available storage. Even so, Time Machine stores snapshots only on disks that have plenty of free space, and it automatically deletes snapshots as they age or as space is needed for other things."

About Time Machine local snapshots - Apple Support

3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite.