The initial recall had been for seats produced and sold between 2009 and 2013. In a notice [PDF] dated March 7, the company explains that some of the additional 403,222 seats were manufactured before 2009.
Seats added to the recall, from model years 2006 through 2014:
Argos 70 Elite,
My Ride 65 with Safety Surround,
My Size 70,
Head Wise 70 with Safety Surround,
Smart Seat with Safety Surround.
The problem with these seats is that the buckle can become gummed up if food or liquid gets into the mechanism. Some parents have been unable to unlatch the buckle under such conditions and have had to cut the harness in order to get their child free.
Graco is offering to replace the buckle with a new design, free of charge. Registered owners will be notified beginning around early April 2014, and offered the free replacement buckle. All other owners may contact Graco at 1-800-345-4109 (toll-free) or 1-330-869-7225.
In addition to the recalled seats, Graco has previously said it will allow owners of an additional 1.8 million car seats not yet involved in the recall to get replacement buckles.
Recall Notice [NHTSA]