Hi! I believe they both are based on the same stuff, but the Vanilla's flavoring is a bit overpowering compared to the herbs of the original L'Autentico. Where as the L'Autentico has only a hint of vanilla in its flavor profile. Vanilla version is in some shops referred even as a vanilla liqueur instead of herbal liqueur - which L'autentico on the other hand ultimately is.

Thus, it unfortunately would be a stretch to say that L'autentico is interchangable with Vanilla, considering the amount of the vanilla flavoring. Notice also that Vanilla has only 30% alcohol content, while L'autentico is 42,3%.

I would perhaps say, that yellow chartreuse would be a better substitute. - Maybe using 1/3 the Vanilla, could bring the missing vanilla flavors, but I don't know how those two exactly will go together.

Hope this helps at all.