This did get straightened out eventually but resulted in quite a few pulled hairs and I would like to know the reason why it happened in the first place.  That is, if anyone's encountered this.  While making a few buildings (in FSDS V2) I created a new texture file, 512 x 512 pixels, in order to include several building faces within the one texture.  This has worked fine in the past, and in fact this particular texture worked fine until last evening.  Today another detail was added to the same texture and saved using DXTbmp in DXT3 format.  The latest detail was then mapped to a new building, and did not show up in the FSDS design window.  I re-opened the file using DXTbmp and the added detail was there, but when opening the FSDS texturing window once again, it was missing!  It seemed the previously-saved texture was being read by FSDS (and also when tested in FS9), however it had since been overwritten, as noted above.  All the other buildings using the same texture displayed without problem.  I then copied both the regular and night textures, saved them under modified names, and changed the file texture names in the FSDS window to correspond to the new textures.  At first, this worked fine for the day textures, but the night ones now would not show up!!  Finally, the original textures were once again copied and pasted into new .bmp files and yet another name was assigned to these.  The FSDS files were once again adjusted to use the re-modified texture names.  Everything now works properly.  For the record the file names were named properly (e.g., the night textures retaining the same file name but with _lm appended), the pixel size was verified at 512 x 512, and they were saved in .bmp then transferred to DXT3 format.  Quite a few new textures have been added, wondering if this may have anything to do with it?  If anyone has any thoughts I would be happy to hear them.