TOC chapter number being skipped

This may sound like 2 separate questions but I don’t know if they are possibly related. i.e. is my approach causing my problem.
What is the best way to generate a Table of Contents when not all the entries are numbered chapters?
I have sections, like preface and appendices, that are not numbered but I want them to show up in the TOC just the same.
What I did is set them up with a different paragraph style name and put that style in Tool>Chapter numbering as level 1. For level 2, I used my chapter Heading style, For level 3 I setup another style which contains the chapter descriptions seen in the TOC. That all seems to work fine BUT I’m having a problem which may or may not be related to the way I set it up. The chapters are numbered fine until it gets to CH 6 which is numbered 7, CH 7 is numbered 8 and so forth. What could be causing this? and this brings me back to my first question. Thanks for any feedback.

I answer here for unnumbered entries.

The Heading n paragraph style family defines a somewhat special list.

Its numbering is based on the “standard” numbering engine, therefore all the tricks and procedures available with lists are allowed in chapter numbering. What makes this chapter numbering list “special” is the fact that you have a separate paragraph style per level while normal lists have a single paragraph style over all levels.

If you want unnumbered headings without disturbing chapter numbering, put your cursor at the beginning of your heading (left of first character) and press Backspace. The number is removed; your entry becomes unnumbered but remains a Heading 1 (or other level), so that you don’t fiddle with Tools>Chapter Numbering.

For the chapter number being skipped, I can’t tell without a sample file.