Hrm.  I'd added orig_tstamp to solve a problem that I've forgotten now.  Perhaps the commit history says why?  Nope. ... Ah, right, we need to keep track of the difference of tstamp for comparison for freezing purposes vs. tstamp that's visible to the outside world (because that tstamp can be used for expiration purposes, and merging a key shouldn't change the user's expectation of when that key will expire).

Hrm, do you mean the oldest sibling?  That would be the sib at the end of the list, not the first on the list.

If I use this hack patch to check the sib at the head of the list, https://gist.github.com/slfritchie/324d955b53b1a581352f , then I see "Diff @ line 725" typically once per minute.  If I change line 725 to look at the tstamp of the sibling at the end of the list instead, then I also see "Diff @ " messages.

So, that's a brute-force approach to suggesting that the answer to your question is probably "no".  But it's quite possible there's a flaw in my hack.