Retrieving Time Machine backed up files I have a Time Machine drive which was previously used to back up my old Mac. Since that machine died I'm using it to back up my new Mac. This means there are two folders in the time machine's backup folder - one for the old machine, one for the new machine.

The new machine's Time Machine app does not show me the content of the old machine's backups.

I would like to rescue/extract the important files (such as Pictures folders etc) from the old machine's backups.

I know TM files are not stored contiguously but as it does not provide a granular management tool, is there a way to extract/copy files from a Time Machine history which the current machine does not see?
You can use the Migration Assistent found in Application/Utilities folder. This program will allow you to copy files, pictures, folders, programs, settings and more from a Time Machine backup. 

Edit:
Open Migration Assistent and choose Time machine option, then click continue. Connect the time machine backup disk and choose it from the menu. Then select things to copy. 

Read more here:
https://support.apple.com/en-us/HT204350

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Restore files from Time Machine to a different Mac