The original KJV translation was from the Vulgate, with comparisons to the (few) Greek texts that were around to compare it to.
That last was an error.
The earlier English Bible translations, were Vulgate translations. The KJV used Erasmus' version of the textus receptus.
Not that it really makes a difference, frankly, because there's no substantive difference between them.
But when we've got folks claiming that the Gospel of Thomas was in the Bible, etc., it's important to get the history at least a little bit right. Apologies for the error.
I assume you are refering to the Itala, and not the Latin Vulgate produced by St. Jerome. I don't agree. But I give leeway in that a number of manuscripts such as the ones Erasmus and Stephes used where must probably along the same lines, e.g. very close word for word, as the original greek manuscripts that where used to create the Itala. Some books I own go as far as saying the greek manuscripts that where used for this version date back to 150AD. And we know the third century Waldensian used this version, before it was basically outlawed and a certain church attempted to exterminate these peoples living in those valleys. But lets face it, most references indicate the 1611 KJV was based on already good translations mixed with GK manuscripts Erasmus had on hand that closely followed the Stephen,Beza, the Elzevirs translations and GK manuscripts.
Incidently I have a great English/Greek Transliteral Bible based on the Stephens text. But that is beside the point. You are probaby very well aware there are so many sources on who transcribed/translated what and by whom, that often paint a somewhat confusing picture. So I will close by saying that my studies in the past would lead me to no other believe that the Itala represented fairly well what the autographs may have contained. But I have not found proof where the committee used the Italaas a key source.