Use Heading Styles or make your own?

[sunalta]

I have Word 2010 on a ASUS G75V using WIN 7

I was handed a document in which the writer did not use the Word built-in heading styles and created his own instead.


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This company has newer docs which use the built-in heading styles.
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My question:
In which version of word were the built-in heading styles first introduced?
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Can I join both types of docs into 1 manual and generate a TOC?
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It's my understanding that chapter numbering does not work unless all the docs use the built-in heading styles. Is that still correct?
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