I'd have to say that the Sproat quotation seemed clearer and less ambiguous than the Costello quotation.
I don't really want to press the point because discussion in this topic has already gotten somewhat more heated than we would generally like. But within the context of the entire "The Lovable Vampire" article, it's actually clear that Costello is referring to a backstory and bio of Barnabas, or at least the character that would become Barnabas. Also, Costello refers to Wallace having written a "bio" not bios, which would have been the more likely word choice had he simply been referring to the character bios of Vicki, Liz, Roger, etc. in the Shadows on the Wall bible.
Who knows? Perhaps Wallace simply wrote a backstory and bio for a potential vampire character and then Sproat et al. used it as a starting point with which to build upon in their marathon session? Perhaps no one account presents the full picture. But I would submit that Costello's remarks would seem to make it clear that Wallace did in some way contribute to the creation of Barnabas and that Wallace's backstory for the vampire character was used as a basis for what would eventually be done with Barnabas prior to the 1795 flashback.
Truthfully, only the people who were actually involved in Barnabas' creation know the entire and complete story of that creation. And dissecting their every word in search of hidden meanings and alternate interpretations, as well as accusing someone of outright lying, is fairly pointless. In the larger scheme of things, isn't all that's important is that Barnabas, by whatever manner he came to be created, became a part of the DS canvas?