I'm seeing a lot of really cool builds coming up, but then after clicking through multiple predecessors it turns out they are just a slight modification of someone else's upload. Sometimes they even get several times more upvotes than the original simply because the successor is from a newer account, so people seeing it justifiably find it way more impressive (without knowing most of the work came from someone else).
I have absolutely nothing against modifying builds, in fact I encourage people to do it, and I also believe that in most of these cases the users didn't have any ill will or didn't even know about the successor/predecessor system (and I also believe that most people wouldn't really care if someone did it to their upload).
But nevertheless I wanted to share this extremely simple tip that many of you probably already know about - how to give proper credit to a predecessor build if your upload isn't a direct successor.
Each upload on the website has a unique ID that you can see in the URL bar of the upload. For example, my latest upload has the following URL:
simpleplanes.com/a/l5dJ0C/DAC-55-100
In this case l5dJ0C is the ID of the upload, and in fact you can completely remove the trailing name of the plane and the link will still correctly redirect to it (which is why old links still work even after a plane is renamed).
This ID is also what is used in the successor system. If you download someone else's (or your own) creation, the ID gets downloaded with it, and stored alongside the design. Then, when you go to upload this design, the game will see that its ID matches an already existing upload, and as such is marked as a successor.
Of course you probably see the "problem" now, this really only works once. If you go on to download a creation that already is a successor, your game will only store its ID and not the original predecessor's.
If you want your final upload to give Auto-credit directly to the original predecessor ("skipping" all the unlisted uploads), you can edit this ID manually in the xml file stored on your device that contains your design.
You can find the xml file in the following directories:

• Windows: C:\users\<user>\AppData\LocalLow\Jundroo\SimplePlanes\AircraftDesigns
• Android: <storage>/Android/Data/com.jundroo.simpleplanes/AircraftDesigns
• Linux/Proton: /home/<user>/.steam/<installation>/steamapps/compatdata/397340/pfx/drive_c/users/steamuser/AppData/LocalLow/Jundroo/SimplePlanes/AircraftDesigns

The filename will be the name you used to save the design followed by the xml extension.
Make sure you first save your design in game, then you can open its file in any text editor, even just notepad. Right on the second line you will see a url= entry, this will contain the ID of the predecessor (or it will be empty).
You can paste the ID of the original upload into this between the two, so for example if I wanted to make an aircraft design a successor of this, I would make sure the entry reads exactly url="l5dJ0C".
After the file is modified and saved, you have to reload the plane in the game, so the new ID is applied. Once that is done, you can upload your final design and the Auto-credit should point to whatever ID you put in its file.
If you do a modification like this, I recommend you also upload your design as unlisted first, and only publish it after you make sure the Auto-credit works as intended.

This isn't only useful for properly crediting original uploads, it is also handy for example when you forget to make your challenge entry a successor.
An alternative solution to manually editing the file would probably just be disconnecting the main cockpit of the plane, saving the entire thing as a subassembly, and then loading the original and replacing its entire design, but that can get pretty impractical, so I personally prefer this way.