I got this information from an English Website dicussing the history of camera, English products in particular. Of course I wasn't smart enough to bookmark the page. But the referral to "full plate" was in direct reference to the introduction of the 15X12" camera in 1907 in England.
"In 1907, Thornton Pickard listed the "New Model" in sizes from 1/4-plate to 15" X 12" and the original model in sizes from Postcard to 10" X 8". Apparently the original models offered were unsold remnant stock since they carried very low prices."