use:
<ol start="
50">
<li>...</li>
<li>...</li>
<li>...</li>
</ol>
at the beginning of each numbered list where
50 is the starting number.
Be advised, I think there are still some devices/apps that don't honor the "start" number. If you want the widest acceptability it is better to include the number manually:
<ul>
<li>24. yadda</li>
<li>25. yadda</li>
<li>26. yadda</li>
</ul>
Cheers,