A practical tip that works miracles on 5.25 diskettes: rub their edges against a table top or whatever, making them sit looser in their sleeves. Does miracles to disks that cause read errors - strange as it sounds.
Also, using an 80 track drive to read a 40 track disk works most of the time. But if you get any read errors, trying with a 40 track drive solves a lot of them!
Lastly, have multiple drives. A read error on one drive might not be a problem on another drive.
I recovered more than a thousand floppies some years ago. And learned that read errors in most cases are not irrecoverable. Try another drive, rub the diskette's edges - the two things that fixed most problems.
Also, using an 80 track drive to read a 40 track disk works most of the time. But if you get any read errors, trying with a 40 track drive solves a lot of them!
Lastly, have multiple drives. A read error on one drive might not be a problem on another drive.
I recovered more than a thousand floppies some years ago. And learned that read errors in most cases are not irrecoverable. Try another drive, rub the diskette's edges - the two things that fixed most problems.