A number of files on this disk are corrupted. My reading of the disk
did not have any errors so it appears the corruption happened when the
disk was being written.

EDU25.PA had a small corrupted section. It was corrected by comparing
with the other versions. The bad data on the disk was shifted by one bit
so I could verify that the correction matched the original file contents.

EDU253.PA had five sectors of bad data. I fixed it by copying the missing
code from EDU25.PA. The length of the copied code matched the corrupted
code length but it is not possible to verify that the code is identical to
the missing code section. The bad data appears to not be related to the 
proper contents in this file. Many of the words are 0000 and 7777 and the
others don't seem to be any variant such as shifted data of the expected
contents. The editing of the file also changed slightly the formatting.
There were a few locations where the file had CR LF CR. The extra CR was
removed.

EDU20S may use symbols that aren't defined under all PAL. You can build by
creating file tape.pa with
	DTXA=6764
	DTCA=6762
	DTSF=6771
The build with
.PAL EDU20S.BN<TAPE.PA,RKA1:EDU20S.PA

A number of other files are still corrupted. There is insufficent information
available to correct them. For some of the files text after the bad blocks
can be viewed by selecting more then display PDP-8 8 bit packed characters as
text.