The original authors had the right to prohibit distribution of that
material, and some (myself included) have asserted that right
vigorously. I.e., it's not merely a matter of what was "lost" but also
"who has the right".
Given the history of the broad no-charge distribution of I-D's, should
anyone be so benighted as to try to take this to court, the issues
under 17 USC 107 and 17 USC 108 would be quite interesting. (Yes, I
know those are US laws, but the IETF and ISI are both in the US.)
Have you registered the copyrights in these valuable documents?
R's,
John