Manipulating Dates Automatically in a Headline

[Matt Price <moptop99@gmail.com>]

Hi Everyone,

I've asked this before, but that was a year or two ago and am hoping
someone has an idea now, perhaps involving babel or something.

every year at this time I rewrite a set of syllabi. I do a lot of
moving htings around while i'm oding it, and at the end I have to
enter a whole bunch of dates somewhat laboriously.  I have headlines
that look about like either like this:

-----------------
* Outline
** Week 1: Topic Title (<2013-09-10>)
    Longish Description
*** Reading
- Article 1
- Article 2
*** Lab
*** Notes
-----------------------------------

or like this:
----------------------
* Outline
** Week 1: <2013-09-09>
*** Seminar: Technology and Society  (<2013-09-10>)
*** Reading
- Article 1
- Article 2
*** Plenary: Global Citizenship (<2013-09-13>)
--------------------

I would like to replace the timestamps with code that dynamically
generates timestamps based on the value either in the last sibling
headline, or the parent headline.  It seems to me this ought to be
possible, but I'm not at all sure how to do it.  i would really
appreciate any guidance.  thanks!

Matt