Countermarked 1606 Spanish Coin - What Is It?

Let's fix the pictures first:

Right, now we can see them...

The undertype coin is a copper 8 maravedis from Mainland Spain, dated 1606; the denomination is the "VIII" to the right of the shield showing a castle. To the left of the same shield is a little picture of an aqueduct; this is the mintmark for Segovia. Catalogue reference is KM# 15.5.

Now to the countermarks: one side is marked "XII", presumably the re-valuation mark - the new denomination is "12". The otherside is a crown with numerals that appear to be "164".

Two theories on this one, neither of which I can confirm. At the moment I'm leaning towards the second.

1. Spain's neighbour, Portugal, had a a habit of countermarking Spanish coins for their own use, whenever they found them in change while countermarking their own coins for re-use; these marks often appear in the form of a crown with the new value below. This one is a Portuguese 200 reis re-valiated to 250 reis.

2. Spain itself seems to have done some countermarking of its own coinage, though to a much smaller scale. This other one is just such a coin, countermarked "VIII" on one side and the date "1654" on the other. This fits more with what we actually see on your coin, (I would suggest a date of "1641"; apparently they had a counterstamping done that year) but these countermarks don't seem to be listed in Krause.

Without knowing the specifics of the countermark, I'd hate to guess the rarity or value.