I now have good, salvaged or reconstructed copies of all the original files from Titler's partly-overwritten/corrupted AF117a coverdisk.
All that remains is to repair the directory and file structure of the disk image, so that the original time and date stamps of the directories are preserved and the files can be restored to their original locations.
In theory, this should be straightforward, but it is turning out to be more difficult than I expected. There are several steps on the way to achieving this, but it is imperative that they are carried out in the correct sequence. The problem is that I am not sufficiently experienced at this to know what all the implications of each step are for those still to come.
It's really just a matter of trial and error, but there is infinite scope for this, since I'm working in emulation and each trial starts with the same, original, problematic disk image.
With luck, I should be able to get this resolved over the weekend.
Incidentally, I'm not sure what version of LZX they were using at Amiga Format to produce their archives, because I had to use a combination of Registered versions 1.20 and 1.21 to reproduce their compressed data.