However, some diskettes have shown surface defects in areas with compressed archives (zip).
There are many diskettes. Some of those have defects in areas with compressed archives. There is nothing to suggest that of the many diskettes there are any with defects in areas other than compressed archives.
You failed to parse correctly, the some you quoted is saying that of all the disks some have errors. Not as you suggest which is that of the disks with errors, some have errors in zip archives. The AC was right.
IF I HAD A MINE SHAFT, I don't think I would just abandon it. There's got to be a better way. -- Jack Handley, The New Mexican, 1988.