I’ve been part of a court case with psychiatrists giving expert evidence and this was part of their evidence.I haven't heard this before and keen to know more if you happen to have a link/reference as that's not my understanding of C-PTSD
EDIT TO ADD : this court case was in 2014. Looking at recent research it seems that whilst there is a big overlap in symptoms and the conditions often occur together in the same patient they do distinguish between cPTSD and BPD.