One of the more recent Jill editions returned to pictorial covers. The artist credited is Adrian Lascom. There is an artist called Adrian Lascom, with a website, but his current oeuvre is very, very different to those Jill covers - it “acts as a catalyst for existential contemplation.” It does state in his biography that he has illustrated children’s books, but although I’ve emailed to ask if he did the Jill covers, I’ve had no reply. Perhaps the spam filter ate the query, but frankly, if I’d done these illustrations I wouldn’t be too keen to own up either. Taking the charitable view, I’ll assume there is a completely different Adrian Lascom who did those Jills.