Missing Time Machine Backups after replacing HD's

[quadra605]

Hi,
I work in audio/video post production and because of the wear & tear on my HD's I usually replace them every 3 years with new & bigger drives (and store the old drives off-site). I work on a Mac Pro 5,1 running OSX 10.13.6 and backup everything to an internal 6GB drive via Time Machine.

Three days ago, I upgraded my System drive & two hard drives (giving 2 of them different names from the drives they replaced) & I saw, for the first time, that Time Machine wanted to "Verify backups". I let it do it's thing and didn't think much about it until I went into Time Machine this morning and found all the backups prior to the installation of the new hard drives are missing.

So, I have 3 questions:

1. Is there any way to restore those old backups? Are they hidden somewhere or did Time Machine actually delete them?
2. What did I do that caused this, so I don't repeat it in the future?
3. I'm planning on upgrading the Time Machine Backup to a new 12TB drive, is there anything I should keep in mind about transferring TM backups to a new drive?

Thanks!

 

[KeesMacPro]

AFAIK Time Machine keeps the old backups until the disc is full.
From a while ago I think I remember what happens when you change the names of the discs : TM showed "verify backups" so I assume it changed the names of the discs without changing the content .
If this is what happened, you got a uptodate TM backup.
If TM stored the data with the old disc name too, you could see it when you open the TM backup.

To answer your questions:
1-I don't think they are hidden, but replaced, so I doubt you can restore them.
2-you changed the names of the discs. (and made a new backup afterwards)
3-In case you'd like to keep the old disc ID's, you could not update the TM anymore after the change and leave it untouched. For the new setup you could start a new TM backup on another disc.
This way you can restore to both setups.