This is a question that's been boggling on my mind the past couple of days and I feel like I might want to make a YouTube video on it and actually test it out as soon as I get an external optical drive and an external hard drive to run Windows 98 and XP virtual machines on my computer, and get a physical copy of The Sims Collector's Edition (The Sims + Livin' Large (Livin' it Up in Europe)) and a physical copy of The Sims Complete Collection to load up on the virtual machines.
So, here's what we know so far:
The Sims Deluxe Edition combines the base game with Livin' Large, 25+ exclusive objects, 50+ exclusive skins, and The Sims Creator, all on two CDs. The exclusive objects are found in Maxis/The Sims/Deluxe, while the exclusive skins are lumped within the same folder as the base game and Livin' Large skins in Maxis/The Sims/GameData/Skins.
The Sims Double Deluxe combines The Sims Deluxe Edition with House Party, and a bonus CD with some more exclusive African and Asian-themed skins, objects, walls and floors (Found in Maxis/The Sims/Downloads/doubledeluxe/doubledeluxe.iff) and some of the official downloads from The Sims website.
The Sims Complete Collection combines the base game with all seven expansion packs, the Deluxe Edition content, the Double Deluxe content, some extra downloads from The Sims website, and The Sims Creator, all on four CDs.
The Sims Deluxe Edition can be installed as an expansion pack over an existing installation of the original version of The Sims, whether that version of the base game is already installed on its own or with House Party, Hot Date and/or Vacation (On Holiday in Europe) installed between the base game and Deluxe, as long as Livin' Large isn't already installed first. Installing House Party, Hot Date and/or Vacation on top of Deluxe will prompt the game to require an immediate update of the installed files.
The Livin' Large expansion within Deluxe Edition is not entirely backwards-compatible with earlier base game and Livin' Large installations (http://simania.nl/simania/ssp/simdelll.htm).
The Sims Complete Collection is designed for "all or nothing" installation, so we have to install the whole collection in one go, and we can't choose which packs we want to install and leave out.
Some of the skins and items from Livin' Large, Deluxe Edition and Double Deluxe aren't included in Complete Collection, and some of the Official Downloads sets are missing parts, including the Green Bedroom Set, which originally included a clothes drawer. The missing files can be re-added manually and are still compatible. There's a link to the entire archive of official downloads from The Sims website (https://www.reddit.com/r/thesims1/c..._sims_complete/) (https://modthesims.info/showthread.php?t=689631), but I think it's still missing the Deluxe and Double Deluxe stuff.
The Sims Legacy Collection is just a digital re-release of The Sims Complete Collection and thus has the exact same content, except for the omission of The Sims Creator, so it too is missing the same content as Complete Collection.
So the question that I would like to get some answers for is: Is it possible to install The Sims Complete Collection as an expansion pack over an existing installation of either The Sims Deluxe Edition or The Sims Double Deluxe? If so, will the Complete Collection installation retain all of the Livin' Large/Deluxe Edition/Double Deluxe content, or will it wipe out some of that content without warning? Or will the installation attempt throw some errors requiring us to uninstall Deluxe Edition or Double Deluxe and then clean install Complete Collection? And will it be possible to create an archive of the missing Livin' Large/Deluxe Edition/Double Deluxe content to paste directly into the Complete Collection and Legacy Collection via Program Files?

So, my answer here is... I think so, as long as you don't already have Makin' Magic installed.

The thing about Complete Collection is that, unlike Deluxe, there's no flag to check for it. There's also no ranger.iff associated specifically with complete collection (RangerD.iff is associated with Deluxe). If you screw up your install of Complete Collection the game thinks it's just Makin' Magic + Deluxe + all expansions.

So, as long as you don't have Makin' Magic, Complete Collection should install just like you're adding on a new pack. I don't think it'll remove anything, since installing Makin' Magic wouldn't remove anything. If you install packs 'out of order' it always asks to "finish" with the newest pack after installing the content. You can do this with any arbitrary combination of packs.

I think the missing content is already "loose" (not packed in a FAR file) which is why it was overlooked to begin with in Complete Collection.

Can you list which objects are missing? other than the dresser?

I'm pretty sure the branded items are missing-- Pepsi Machine, Intel computer, McDonald's food cart. Also the dorm furniture was only ever available though the website as far as I know (never included on any disc) so I'm not sure if we want to count that as "missing".