exco has decided to essentially leave the Cuban defector language as it is in the league rules. This means that any player who defects from Cuba, regardless of age, will fall under this portion of the rule....If the player is a Cuban defector or is from another professional league such as Japan, Korea or Mexico and does not sign a contract with an MLB team by opening day (Opening Day of the 2007 season in the example above). If the does not fall under one of these two categories, he must have signed a contract with an MLB team prior to January first of that year (prior to January 1st of 2007 in the example above).
For example, if a 17 year old Cuban player defects and subsequently signs with a major league team before opening day of 2010, the team that drafts him will retain his rights. If he is not drafted, he will be eiligble to be signed immediately after he is signed by an MLB club up to opening day and can be signed at any time thereafter.
Chapman and Arguelles obviously fall into this category.