Royal Doulton Character Jug - Walrus and Carpenter

This is a Character Jug made by the Royal Doulton Co.  It is from the Alice in Wonderland Series made between 1965 to 1980.  I have looked at a few of these Walrus and Carpenter Jugs on the internet.  I have found they were made in 3 sizes (2 in. tall, 4 in. tall, and 7 in. tall).  Each size has a corresponding "D" number.  This character jug measues 7 in. tall.  The 7 in. size is suppose to have a D 6600 number on it.  This one has a D 6604 number which is the 4 in. tall size.  Not sure what to think about this.  Can anyone help determine if this is a real Royal Doulton or a fake?  Thanks