Questions on Disk ][ error checking

[dog_cow@macgui.com (D Finnigan)]

I have a question about the error-checking mechanism used on the Disk ][.

As I understand it, checksums are used to verify that the data read from the
disk are valid and error-free. However, would there be a way to skip these
checks? Is there any software that does so?

I ask because I have more than one disk which has some data and programs
which can be read successfully, and some data which cannot. These disks are
not copy-protected. Would it be worth my time to make a disk image of a disk
with only partially good data? Is this even possible?

Also, would there ever be a circumstance where the disk has become damaged
in an area such that the Disk ][ cannot tell whether a bit is 1 or 0 and
thus refuses to read that disk?