From the rare Australian cover at the Museum of Adventure Game History. Given there’s only one pirate in the game, it seems to imply you’re the one on the left.
So “Beginner” as a difficulty was right. Perhaps “confusing plot-wise” might also be apropos.
The pirate I mentioned in my last post is indeed the missing crew-mate. You find him sleeping in your flat.
Perhaps he’s the same teleporting one from Adventure? In any case, I’m not sure why he’s all happy at helping you. I almost suspect there was some missing conversation from before the adventure started, but why would he be grouchy at taking your treasure chest then?
So having the pirate on board allows you to sail to Treasure Island.
(Click the image if you want the complete game map.)
Following the map conveniently obtained from the pirate’s treasure chest you can dig up a box with a shovel. The box has … rare stamps? Not what I’d associate with pirate treasure, exactly.
The other treasure involves braving typos:
My dictionary weeps.
The snakes will kill you if you try to take the treasure. However, the helpful mongoose from earlier … is apparently not a mongoose, and if you try to use it, you will end up with a “dead squirrel”.
The parrot, on the other hand, will chase the snakes away, again just like in Adventure.
I liked the parrot so much that I took it home with me in triumph.
You may plausibly ask, what happened to the pirate? Well, he got drunk again, then after I woke him we sailed back to Pirate Island and I went home and got the screen above. He didn’t seem to care about the treasure. I guess for him, rum was the real treasure.
Renga in Blue 
In Pirate Adventure, the London flat belongs to the pirate, not to you. That is why he returns there after you give him rum. The clue is that the attic has a pirate’s duffel bag and broken rum bottles in it at the beginning. It probably used to be Long John Silver’s flat. Also, you can catch the fish in a rum bottle, which negates the need to wait for the tide, (wear the water wings).
oho! That’s kind of like how the Count starts the player In Media Res — I guess the player broke in for fun? To find treasure?