It sounds like you did what I was suggesting - putting something like $post[postcount] in the template to see what gets spit out. Unfortunately, I don't understand what this output page is you are talking about. If that variable works in the template, isn't that where you wanted to use it? You could do what you were saying in the postbit_legacty template by just wrapping it all in a condition, no?
HTML Code:
<if condition="$post[postcount] == '1'">
<li class="updates">
$template_hook[postbit_start]
$template_hook[postbit_messagearea_start]
<p class="update-date">$post[postdate]</p>
<p class="update-message">$post[message]</p>
<if condition="is_member_of($bbuserinfo, 6)"><a href="$post[editlink]" name="vB::QuickEdit::$post[postid]">Edit</a></if>
$template_hook[postbit_end]
</li>
<else />
something else
</if>