Can Sherlock Holmes be trusted?

I do think Lupin is a better target, especially for the Japanese audience - Enola, not being part of Doyle’s original canon, would be a very poor twist for people not oddly familiar with what basically amounts to mid-budget Sherlock Holmes fanfiction from 2006 in a different language.

As for copyright, the Doyle estate is only set to lose the last of their copyright over the latest original Holmes stories later this year, and they’ve been very vigilant in using any leg they can find to get a buck out of anyone they can, and the easiest way to dodge them is to basically avoid the original Sherlock canon as aggressively as possible at every turn (by, for instance, inventing a teenage sister), which comes with the very convenient side-effect of making your work original enough to copyright independently, as is the case with Enola. Interestingly, this is also why the more faithful adaptations tend to come in waves - as iconic individual stories like The Final Problem had their copyright protections expire, people made very carefully crafted works to use only elements from the public domain stories and not integrate anything from the ones still protected, to avoid finding trouble with the overly litigious Doyle estate.