<p>(<em>+1 for the massive research effort if nothing else; note that upvotes &amp; downvotes have a different meaning on meta than the main site: here they imply people agree or disagree with your proposal.  In this case, I partially agree, so it goes with the admiration for the quality of the question.</em>)  </p>

<p>Let me put down some random thoughts:  </p>

<ul>
<li>Regarding the question about old tags not showing up in searches, I believe that issue has been resolved.  (For example, if you look at the answer I linked to in the comments, the corresponding question is now tagged <a href="https://stats.stackexchange.com/questions/tagged/logistic" class="post-tag" title="show questions tagged &#39;logistic&#39;" rel="tag">logistic</a>, so it can be found.  I gather the moderators have changed the protocol when making duplicates somewhat so that this problem no longer occurs.)  </li>
<li>I believe I'm agreeing with @AndreSilva (at least partially) in that there is room for two kinds of meta questions here.  The thread <a href="https://stats.meta.stackexchange.com/q/1200/32036">Current tag synonym candidates</a> is a good choice for simply proposing a candidate synonym.  Of course, you can do this through the mechanism SE originally set up, but you need 5 upvotes on the tag in question, and it will never get noticed or resolved.  This way makes it more salient and more democratic.  </li>
<li><p>On the other hand, some of the potential duplicates you list strike me as primarily <em>discussion items</em>.  That is, the OP is not necessarily certain, but wants to find out what people think about the overlap / distinction between the two tags.  Prime examples of this type might be:  </p>

<ul>
<li><a href="https://stats.meta.stackexchange.com/q/1659/32036">What is the difference between tags &quot;validity&quot; and &quot;validation&quot;?</a></li>
<li><a href="https://stats.meta.stackexchange.com/q/1817/32036">Do we need both &quot;power&quot; and &quot;power analysis&quot; tags?</a>  </li>
</ul>

<p>Note that neither of these seem to be quite saying 'this is obviously a synonym, can we make this happen?'  </p></li>
<li>Regarding your points about deleting answers to <a href="https://stats.meta.stackexchange.com/q/1200/32036">Current tag synonym candidates</a>, I still think they should be.  

<ul>
<li>First, if we do end up using that thread as a bulletin board for this issue, it will become excessively cluttered very quickly with old, resolved proposals, too cluttered to maintain its usefulness.  (Remember that new answers will all be stuck at the very bottom, which will get further and further away.)  </li>
<li>Second, once a tag has been made a synonym, it makes little sense for people to keep voting and discussing the issue; the old tag will simply have disappeared.  Should someone in the future want to revive the old tag, the best bet would be to initiate a new meta.CV thread to discuss the issue.  Moreover, I'm not clear how the process of unmaking a synonym works.  The moderators may be able to do it, but I don't think it's ever been done before, and if you read through the comments to <a href="https://meta.stackexchange.com/questions/135466/how-can-you-find-questions-with-ses-search-features-that-have-now-defunct-tags">How can you find questions with SE&#39;s search features that have now-defunct tags?</a>, @whuber's reservation was that the proposed solution makes the change irreversible.  Since that approach appears to have been adopted, it seems even more unlikely that synonyms will be converted back.  </li>
<li>For what it's worth, I have deleted many of the answers that I had posted to that thread, where the change was made.  And you should have the ability to undelete your answers if you feel the need for some reason.  </li>
</ul></li>
<li>Many of the threads you list probably are duplicates and could be closed.  However, I'm not sure if it is as important to do that with old meta threads.  Here on meta, the community user does not bump unanswered questions.  If no one else is bumping them, it may not be worth the hassle to close them all.  Naturally, <em>new</em> threads that are duplicates should be closed.  </li>
</ul>
