Here's another view of a saturated balsa core. As you can see the balsa actually looks wet and you can physically see the moisture.
One should note that this balsa, even in the present condition, still adhered quite well to both the top and bottom skins and required a screw driver to pry this square from the rest of the deck. At some point this would have failed. Even this wet, the deck was still sounding out with minimal differences in tone. To the untrained ear, without a moisture meter and only a hammer, one might assume this deck was in A1 condition.
This is a good example of why spot soundings and moisture readings should always accompany one another.