Thanks, dandl-- I believe the issue is close to resolution, and (as mentioned above) appears to be hardware related. After SFC reported it could not find a Windows installation anywhere on the W7 boot HD, or on even other HDs in this system, it became almost obvious I have a very rapidly degrading boot HD recording surface.

This boot HD is well over 15 years old, but like most enterprise-origin SCSIs, is built like a tank and is capable of running for a long, long time in its assigned role. The HDs latest history, however, is one of requiring a chkdsk at least daily after various processing anomalies, usually a freeze or delay. On completion, chkdsk often finds and repairs a scrambled index and occasionally lost files. Chkdsk never has reported a bad sector, however.

What led me to pursue possible recovery is this old (pre SMART-era) Fujitsu SCSI U160 still runs and passes its own media validation test from its Adaptec controller. Whether that test corrects an error condition like this one while retaining viable data is impossible to determine, since it does not report findings and remedies. Safer to presume the HD-- at least, physically-- is no longer reliable.

Before the HD is discarded, I am screening the disk surface sector-by-sector with SpinRite 6.0 simply to re-record all marginal data, before finally imaging the volume.

* I noticed you also have discovered there is plenty of life in older computers, if the operator knows how to put that hardware to better use than running the latest Windows. Although I am not a Windows-basher (this problem, for example, no longer appears to originate in the Windows file(s) system), Linux gives surprising and completely acceptable new life to the majority of older equipment. And to the point Linux might be considered its natural environment.