I don't think there is anything wrong with you asking the question.
That said, the Lambsfoot blade is likely one of the most oft misunderstood (and therefore misidentified) blades out there. Same could be said for Kepharts, which we won't discuss here, but countless makers make a "Kephart", only to have completely misunderstood what makes a Kephart, a Kephart.
The thing is, the Ancient Barlow is not a Lambsfoot. Being a SFO of Charlie's, it was never billed as such but it was meant to represent a very distinctive blade style on a very distinctive and old pattern. But I get why you think it might be a grey area - even I have issues with some of the knives that are accepted as proper "Lambsfoot" knives.
My comment regarding "if one has to ask" still holds true. If you are holding a knife and you have questions regarding its legitimacy as a proper Lambsfoot, then chances are it's not going to qualify. I think a great many of us have been there and done that and through experience and enthusiasm, we've learned a great deal.
Again, questions should be welcomed. My point is still that once you become familiar, and this comes from experience (and hanging out here), it will be hard to mistake otherwise.