After looking thru the last pages of 1956 Motorola catalog here....
http://www.flickr.com/photos/hollywo...ith/3427553041
I was surprised Motorola was still advertising the 19 inch color models considering that the other guys were making 21 inch models. There was no mention of upgrading their sets with the 21 inch kit.
Also, I thought the 21 inch Motorola 21CT2 was out in '56 as there was an advertisment for this model in the 1956 Life Magazine. I think it was during the May '56 edition...I have this May edition at home. I guess this means the 21CT2 was a 1957 model... not a '56.