As it turns out, your reply matched exactly what I had already
done, so it's good to know that I was on the right track. The
details are that I have a button labelled "Next Error" which locates
the next line in the list box which has a potential problem which
needs to be evaluated by a supervisor, which is the same idea as
putting a 'tick' in a selection box. I should have said that
before, so your reply is on target, indeed, thank you.
And, it is also good to know that the listbox  lines are limited
in that way . . . I had thought I might be missing something, but
apparently that is not the case (for once, <grin>).
Have a wonderful Thanksgiving Day, if you are in the US,
otherwise, have a wonderful day wherever you are.