Louie points out to Scrooge that he can swim through money after the older duck tells him that he'd hurt himself doing it. Scrooge points out that he had to build the muscle for it and thus trained himself to do it. Given the feats in the comics and past cartoons, which this show heavily bases on, it'd make sense that a guy who can destroy a Steam Boat with his bare hands can swim through metal with ease; he's just shrugging it off. And it also makes sense that he wouldn't let Louie, who's a lazy and mostly apathetic kid, do something so dangerous since he does care about his family.
Of course the Number One Dime exposed in the reliquiary is a decoy: with Magica after it, it's perfectly normal that Scrooge keeps decoys around.
Also, the comics already had someone spend the Number One Dime-if it happened here too, Scrooge won't keep the real one where it could happen again.
Theres hardly anything about Della in Scrooges archives. She's hardly in the comics, too.
The plot of this episode gets kicked off when Louie needs an extra ten cents for soda that should normally cost a dollar. Of course a cheapskate like Scrooge would charge an extra ten percent at the vending machine.
Despite saying that she was cooped up in the mansion all the time, Webby has clearly been to the Money Bin with Scrooge a few times, as Quackfaster recognized her and told her that she was not getting into the Archives, and in such a way as to suggest that this is hardly the first time that Webby has made the request. Scrooge has been allowing Webby to tag along with him for some time, now, and not just letting her live in the mansion as Beakly's ward. The only reason Webby hadn't seen more adventure before is because Scrooge was effectively retired.
Scrooge boasts that he doesn't spend a penny more than is necessary (and if you remember Magica from the original series, $15,000,000 for magical defense might seem like a bargain), but then you have to account for the fact that McDuck Manor has "a dozen or so" spare bedrooms. Why would a confirmed bachelor like Scrooge need that many rooms, which would have surely cost more to add to the mansion, if he's so thrifty? Simple: prior to the Spear of Selene incident, Scrooge was very big on family. Donald and Della adventured with him frequently, and he had portraits of his own family from Scotland all over the place. He may well have been looking forward to having a large, extended family living with him before the incident ten years prior that effectively had him go into retirement.
Also according to Word of God, Donald and Della's parents (Hortense and Quackmore) both died when they were still fairly young. It's quite possible that Scrooge was the one to raise the twins and they used to live in the manor with him until the Spear of Selene incident.
The Archives at the Money Bin still use a card-based catalogue despite computers being much more effective. But someone as obsessed with her job as Emily Quackfaster would not allow a computer do it for her.
Why does Scrooge keep Emily Quackfaster and Gyro Gearloose on the payroll when they're both clearly a few cards short of a deck? Because, as in the comics, Quackfaster is extremely loyal to Scrooge, and is his longest standing employee, having been brought on board by Scrooge's sisters decades ago. As for Gyro, he had a grandfather in the comics who was Scrooge's first friend in America, and to whom Scrooge feels he owes a great deal. Gyro's employment with Scrooge is probably entirely by grace of that legacy.
When the vultures complain about Scrooge buying a $5,000 velvet pillow as an unnecesary spending, he explains that it is for his first dime, which is too valuable for him. But at the end the dime is revealed to be a decoy, he carries his real first dime with him at all times. So the vultures are actually right on this one.
Scrooge tells Louie that he could crack his skull if he jumps into the money bin without the proper muscle training. Louie later does fall in and isnt seriously hurt, but it clearly did hurt and he does have trouble moving through the coins. The same thing almost happens to Gyro when he nearly gets tossed in during Lil Bulbs rampage, and you know a twig like him would have probably broken every bone in his body.