I am also a bit confused by the term "stability." Other than numbering and the Master Documents feature, Word documents have been very stable since Word 2003. Numbering can be made stable but the buttons on the toolbar/ribbon don't help.

A multitude of styles does not make a document less stable; it may make it harder to edit. Multiple numbering lists are sometimes needed because you can have two lists that are really intermingled. Having those lists attached to styles, though, is vital if you want to be able to edit them in the future. How to create numbered headings or outline numbering in Word 2007 and Word 2010
Changing the start of numbering is sometimes done to indicate that certain parts have been deleted; you keep the original numbers from the original document so references to that document elsewhere make sense.

Style-based formatting is far preferable to direct formatting.

Under no circumstances should the Master Documents "Feature" be used routinely or on documents that are going to be further edited.

The problem "char" styles do not develop in Word 2003 and later but may be inherited.

Documents should not be used as the source for new documents. Period. Templates should be developed for proposals. The chance of error rises exponentially basing documents on other documents based on other documents.

New versions of Word allow limitation on styles to be used. See Chapter 50 of Herb Tyson's Microsoft Word 2010 Bible. Note that this also limits ability to add section breaks. This is on the Review Tab (Restrict Editing) or the Developer Tab.

A key thing is numbering. That is most likely to raise problems in documents that go through heavy editing when the numbering is not properly based on Styles.

One option on numbering is to use SEQ fields that are incorporated in AutoText entries. This is essentially bulletproof.



You may want to modify the Ribbon in your templates to completely remove the bullets and numbering buttons (or attach them to SEQ fields and AutoText in some fashion). Removing the buttons is relatively easy. These modifications, though, are done using XML editing, not through the Modify the Ribbon commands in the user interface. Customize the Ribbon (It doesn't take rocket science).

With these modifications, you can also limit access to other Word features from most users.

Probably the biggest cause of document corruption in the last five years is people trying to edit (or save) documents on flash drives and DVD-RW. Word does not work well with mobile media; never has.

Thank you both for your thoughtful responses.
The nature of the business I'm in involves documents going through a number of hands in a rather uncontrolled environment. For instance, for any given five or six authors on a proposal, three may be working in 2007, the others in 2010, or perhaps one or two in 2013, all on their personal computers out in who knows what hinterlands here or abroad. Thus, there are practical limits to what we can do to make Word set-up on them all the same. I have only met one person in a major corporation of our type so far, who successfully implemented a style-limited template process, using a custom toolbar in a self-extracting-installation template in W2003, and his proposal authors weren't constantly changing.
Although we have a template which goes out to be used for authoring, one carefully created with Ms. Kelly's expert directions and other such expert advice, we inevitably deal with documents returning, at various iterations of the extended process, with text and tables pasted directly from a wide range of sources by folks who simply don't know better. When we can, of course, we move everything cleanly to a new template-based document, but that is not always possible. The erosion to which I referred, is acceptance of bad practices and their effects continuing until too late in the process to rectify. If one author, for instance, has automatic style-updating checked and doesn't notice it's effects...
As to stability, I refer to my repeated experience of receiving documents in which some kind of corruption has been introduced through such uninformed assembling of documents (we do not use master documents in our process, only template-based ones), which may manifest itself in the form of auto-numbering problems, extended tables carrying a host of persisting "ghost styles" with them, and similar things, which can simply make fixing them a long process in a multi-hundred-page document when no time is available for it. I am aware that a long style list is not a problem per se.
Yesterday I had to send out a 350-page "finished" document into which eight older documents had been inserted, each with its own TOC and styles list, some of which styles had the same name but different font and paragraph characteristics, along with numerous instances of Normal text with different formatting, etc. Frankly, I was worried about what might happen each time it was opened.
So, I was just probing, in my post, for whatever consensus there might be on the consequences of bad practices. I will continue to make my case here against them.