UPDATED 6/13:
Players selected in the MLB First-Year Player Draft (MLB Rule 4 Draft) are placed on a club's Negotiation List.
In most cases, a player selected by a club in the Rule 4 Draft will remain on the club's Negotiation List until either the player signs or until the signing deadline (whichever comes first), and if a club does not sign a Rule 4 Draft pick by the deadline (5 PM Eastern on the Friday that falls during the week July 6-12), the player is removed from the club's Negotiation List and becomes eligible for selection again in the next Rule 4 Draft in which the player would be eligible for selection.