<ol>
<li>Had he lived beyond his twenty-eight years, Schiele would have to become a very different artist functioning in a very different world.</li>
</ol>
<p>The error occurs at "have to" because it's not consistent with the past perfect tense of "had." I believe it should be "have had to," but that's sounds a bit awkward.</p>
<ol>
<li>In the eighteenth century a simple method of musical notation helped to make music more popular than in any century.</li>
</ol>
<p>The error occurs at "any century." It should be "any other century."</p>