That's really helpful – thanks. (I take it that the Results key - as well as a Results value - should also be optional ?)
The root example was:
which was reported by others, and experienced by me, to have become broken at some point,
in contrast with yesterday's:
which, on my system at least, now seems to work.
The only change that I was aware of there was adding a Results keys, but I now wonder whether simply removing, reloading and restoring, combined with recompiling the .scpt, was really what made the difference ?
(I have failed, this morning, to reproduce what I thought was last night's result - that removing the Results key from other macros generally inhibited function, as well as generating the error messages)