Anything is possible. I do know that there was much name changing (especially first names) in many Maritime locations of the time. To go from Bertrand to Bernard is entirely possible. Gracianne could also have become Gracienne, Gratia, Grace or even Lucienne, if she wanted to do so. It all depended on what they were comfortable being called or known as. It was not an error in transcription, just which name was more in vogue at the time of the being alive.
I also think the fact that a sister Gracianne was present in St-Pierre is a good indicator that you have the correct family from France, and undoubtedly, these DiThurbides were distantly related to the Magdalen Islands Turbide family (a very large branch), which also originated in Sare.
Best regards, Dennis