I think the -9 value instead of the (+)9 could be a sort of typo. Reason is that the -9 value leads to trim recommendations not being achievable or just on the very edge to it like e.g. '15.0', while the default (+)9 value renders them correct.

The VC indicator may not be the best reference but that green band is the one showing a proper trim (range) for TO. Outside of it, the TO warning horn should sound when advancing the #3 thrust lever. And the mentioned '15.0' is well outside of it, hence my note. On another note. The CS707 1.3 warning horn is inop.  :-/

Well, I could be totally wrong since those findings just arise from observation and I may even be using an improper payload layout. Funny thing is that I've actually missed that small minus sign all the time when reading the readme. It was just lately, with the new mod version, when I finally realized that it has to to be added when following the instructions one by one.  :-[ That's just to explain why I didn't chime in sooner.

In the end, there's a chance that both values are, somehow, wrong. The default one being too far aft forward and the correction then being an over-correction. So just read the note on the +/-9 value as a starting point for the tests you've ran. Thanks for that input by the way.