Thanks Mac. That cleared it up. Well as much as by saying the law isn't clear
The finder must take reasonable steps to locate the owner
Seems clear enough - the instances where larceny wasn't upheld were where un-labelled/ untraceable items such as money were found in public spaces, where nothing about the item or the location gives a lead as to who the legitimate owner might be. Cases where it was upheld were where things are found relating to customers, or transactions or identifiable premises. In your case theres no question where the laptop came from - its got their name on it and arrived in a package with their return address on. So you don't even need to take a reasonable step.
As a contrast. We received a package with some wheel trims in last week. Unknown name but my address (a named house rather than a number and our full address and postcode so its not a typo). Left at the door by the courier, no consignment note or return address, unbranded items in unbranded packaging. I know all my neighbours here, so I know its not for any of them. So theres a limit to what reasonable steps I can take to identify either the intended recipient and no steps I can take to identify the vendor.