Nope. The spine is just a series of references to the ids in the manifest section:

<manifest>
<item id="ncx" href="toc.ncx" media-type="application/x-dtbncx+xml"/>
<item id="style" href="style.css" media-type="text/css"/>
<item id="a_1" href="section_000.html" media-type="application/xhtml+xml"/>
<item id="a_2" href="section_001.html" media-type="application/xhtml+xml"/>
<item id="a_3" href="section_002.html" media-type="application/xhtml+xml"/>
<item id="a_4" href="section_003.html" media-type="application/xhtml+xml"/>
<item id="a_5" href="section_004.html" media-type="application/xhtml+xml"/>
<item id="a_6" href="section_005.html" media-type="application/xhtml+xml"/>
<item id="a_7" href="section_006.html" media-type="application/xhtml+xml"/>
<item id="i_div1.jpg_558" href="images/author.jpg" media-type="image/jpeg" />
<item id="i_enchanted.jpg_334" href="images/covers.jpg" media-type="image/jpeg" />

</manifest>
<spine toc="ncx">
<itemref idref="a_1"/>
<itemref idref="a_2"/>
<itemref idref="a_3"/>
<itemref idref="a_4"/>
<itemref idref="a_5"/>
<itemref idref="a_6"/>
<itemref idref="a_7"/>
</spine>