That's what happened once at a Three Choirs Festival prior to a performance of Louis Spohr's Last Judgement. A lady was asked to move to another seat and replied: "This is my seat. I was sitting here for the Creation and I intend to remain in this seat for the Last Judgement."
He himself called his translation 'iuxta Hebraeos' (from the Hebrew).
According to many historians his prime source was in fact a Hebrew edition in Greek letters (a so called 'hexaplaric Septuaginta').
Be careful: there are different Vulgatas. The one quotet above is the Nova Vulgata, a critical edition made in 1979. The current English edition of the Vulgata dates from 1889.
'Petra' is to be found in mediaeval editions of the Vulgata (8th and 9th Century).
As with many details of the old Vulgata (Hieronymus knew only a little bit Hebrew) 'Petra' could probably be an error.
'Petra' is simply the version of the Vulgate.
But what is even more interesting is the fact that Mulet omitts a part of the original text: Tu es Petrus et super hanc Petram aedificabo Ecclesiam meam et portae inferi non praevalebunt adversus eam.
My (German) source points out that the only specification we have of this instrument dates from 1739 (which means years after Bach left Weimar!).
Some further corrections (in bold type):
There is an 'Urtext' edition of the 8 Sonatas and some smaller pieces, published at Baerenreiter, which can be recommended. Unfortunately, the beautiful Leupold edition of the complete organ works seems to be out of print.