I have not written about the Johannine Comma for some time, but new information has come available, especially regarding the Latin transmission thereof. Here are some preliminary results of my latest research.  

Different ways the Latin textual tradition renders “(they) bear record” in 1 John 5:7, followed by their distribution in the Stuttgart Vulgate

• testes (“are witnesses,“ 14x, none in Johannine literature)

• testificantur (“they testify,” 1x, none in Johannine literature)

• testimonium perhibent (“they provide testimony,” 3 of 4 are in Johannine literature )

• testimonium praebent (“they provide testimony,” none )

• Testimonium dicunt (“they speak testimony,” none)

• Testimonium dant (“they give testimony,” 1x, only in the Vulgate comma)

In his writings, John uses a form of the verb μαρτυρέω (testify) 44 times—a majority of all such uses in the entire NT. It is one of the major themes in Johannine literature. Now, when we look at the Vulgate text, we see that the majority of times the phrase “testimonium perhibent” (“they provide testimony”) is used in the NT are in the writings of John. And this remains the case regardless of what form of the expression is used. And this is, in fact, the common rendering in the Old Latin of μαρτυρέω in 1 John 5, including the several uses in the immediate context of verse 7. I have not yet determined how common it is in translating either half of the Comma, though. Nor where the first usage of testimonium dant is found.