Found it. Much more concise than mine. The best answer is by Jordanlev-

In the Page Defaults, click on a block and choose "Setup on Child Pages" -- this will allow you to add blocks to pages that already exist.
HOWEVER, it is a bit clunky and you have to be careful that it doesn't add duplicates to pages. Basically if the block is already on a page, but wasn't put there by the original page default, it will add a second copy of the block instead of being smart enough to know it's already there.
Also, you unfortunately can't rearrange the order of blocks and have them apply to this "child page setup" -- they are always added to the bottom of the existing area's blocks.

A different solution for this situation that I've been using is to install the free "Global Areas" addon (http://www.concrete5.org/marketplace/addons/global-areas... ), then pick one page on your site to be the "single source of content" for a particular area, then add the Global Area block to the page defaults and point it to that page you decided was going to be the "single source of content", then "setup on child pages" the global area block for all pages except the "source" page you decided upon. Now when you edit content on that "source" page, it will automatically be updated across the entire site -- including moving blocks around within the area.

I wish this were simpler to deal with :)

SOURCE:http://www.concrete5.org/community/forums/customizing_c5/default-bl...

Hope that clarifies things for you.

Best wishes,
Wagdi