In desperate need of help! Most folders missing from drive after pasting files ONTO it!

[Dav!d]

Please read for full context but TL:DR:

Cut-Pasted files from one drive to another.

Target drive now missing most folders and is repoting to have way more free space than it should have, pretty much meaning that those folder are genuinely deleted.

Target drive is now called what the source drive was called. This was a standard Cut-Paste operation through Tera Copy, not a clone.

Source drive seems more or less fine but it reports 790GB of used space when checking via Properties yet selecting all folders and copying them to another drive results in only 468GB of data. There also is a massive folder missing. No guaranteee that I didn't remove that manually, though.

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I have a drive on which I store all my Downloads, Pictures, Documents, Videos and Music. By that I mean that I use those folder as my default Windows directories for such files.

There also is a Other Files, Programs and Games folder on it. Other Files simply contains stuff like .iso, .dmg, .exe and, well, other files. 

I try to install all of my programs into the Programs folder and the Games folder is home to some standalone DRM-free games and also the install location of my Steam instance (my actual Steam libraries are on different drives).

All of those folders are at the root of the drive.

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Now, I recently ran out of space on the 1TB 970 Evo and got me a 2TB 970 Evo Plus.

Just like I did when I upgraded to the 1TB 970 Evo from my old 500GB 960 Evo, I just copy pasted and veryfied all folders via TeraCopy.

This pretty much worked as per usual but it also resulted in a different folder and file count on the target drive. While this is pretty normal for simple Copy-Paste of large amounts of files, I hung onto the original files on the 1TB 970 Evo and didn't format it right away, just in case that I wanted to manually check everything.

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Now I've been using the new 2TB drive since around November 24th as my main drive without issues. 
I gave it the old drive letter Y and the 1TB 970 Evo the letter A to have it be in front of my boot drive so that there is no chance of confusing the two. As for drive names, I just call the 970 Evo and 970 Evo Plus. So they were 970 Evo (A:) and 970 Evo Plus (Y:).

All current letters in my system:

(A:)

(C:)

(D:)

(E:)

(V:)

(Q:)

(Z:)

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Now to the actual issue:

Today, I decided to finally do something about the "unnecessary" and now somewhat outdated copy of my drive (1TB 970 Evo (A:)).

That 'something' was to just select all folders and CUT-Paste it onto the 2TB 970 Evo Plus, the drive that was currently in use. Doing something like that has never really caused me any issues up until now, to be fair.

But yeah, considering that I also have almost all of my programs installed to that drive, this certainly could have caused issues for them.

What actually happened is far worse, though...

I once again used TeraCopy and let it run for a bit. The "Skip All" option was selected. 
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I only let it run until around 0.3% were completed and then stopped it because WHY THE FUCK WOULD I NOT WANT A BACKUP, RIGHT?

It had transfered around 56000 files if I remember correctly but I assume that those are just tiny, not too relevant program related files. As I didn't let it run for particularly long, maybe 1-3 minutes, there was no way that it moved or deleted a lot of stuff.

Anyway, afterwards I just turned off my system and took out my old 1TB 970 Evo and replaced it with another 2TB 970 Evo Plus I had bought at the same time as the first one.
Upon boot, I noticed that the system still showed the old 970 Evo with the (A:) drive letter. 

And what this resulted in is just inexplicable to me. The drive, ONTO which the folders were supposed to be pasted, was missing folders! Like the Programs folder, it was completely gone! I only noticed that when trying to open a program.

I restarted the system and let the disk check (the one that comes up while booting) run.

Now, suddenly, even more folders are gone and the Programs folder reappered and appears to be perfectly functional. All programs that I have tested run fine.

But I now have 1.55TB of 1.81TB free, which is not how it should be. This is 265GB used. I do not remember how much used and free space was reported right after the Cut-Paste operation.

And another thing, the 2TB 970 Evo Plus is now called 970 Evo! It was called 970 Evo Plus, guaranteed!

As for the 1TB 970, it seems fine and fucked at the same time. It reports 790GB free via Properties which could very well be a correct value as I had relocated a big folder when I ran out of space. It was 113GB large.

However, when selecting all folders and checking their size via Properties, it only reports 468GB of data. Copy-pasting them with Tera-Copy only detects 470GB. Oh, and the entire Games Folder is missing. The one that my Steam install resides in. Not sure if I took that thing off of htis drive manually, though. I might have and remember something along those lines regarding that folder but I just cannot understand why I would have done that. That was a pretty massive folder, too.

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Moral of the story that I even had been taught before; Always make backups... My last one was around a year ago, and due to not much having changed in my Games folder I can find out its approximate size. Maybe it makes up all of the missing data, I don't know. I just hope that nothing is corrupted.

But still, can anyone please help me in finding out what happened or on how to fix it? I would greatly appreciate it!