{Lanette’s is the easier one to explain here, and the answer is, yep, I made hers up! If anyone’s wondering, Lanette’s last name partly comes from her Japanese name (Mayumi, which refers to Hamilton’s spindle) and partly from this awesome systems engineer.
The history of Bill’s last name is a bit more complicated because I actually stole it from the official Pokémon website’s episode summaries back when they weren’t as well-written as they are now. Whoever wrote the summary for Bill’s episode pretty much just tried to turn his Japanese name (Masaki) into a western one, rather than use his actual localized name. I just thought at the time that it was about as close to a last name as we’re ever going to get, so I’ve been using it ever since. Long story short, I technically didn’t make it up, but it’s also less an officially given name and more of a translation error.}