OK, I may have a solution for you. I found a bit of spare time, wrote a program, and pushed it up to github. My first attempt at getting a windows program pushed to github, so it's a bit rough.
First, download the executable. You'll get all sorts of complaints because downloading an executable is usually a bad idea, your anti-virus may object, the browser, etc. You are welcome to download the source and build it yourself, which is generally safer, but if you aren't a programmer that's not practical, so you can either trust this link, or not.
https://github.com/Linwood-F/DumpJPGs/raw/master/DumpJPGs/bin/x64/Debug/DumpJPGs.exe
Those who want the project file itself:
GitHub - Linwood-F/DumpJPGs
I'm going to assume it comes down into a folder like this: c:\users\yourname\downloads\ If that's not where you save it, adjust the below as needed.
First, create a place to hold the new files. Let's call that "c:\junk" but it can have any name you like, just adjust as needed below.
Now find your lightroom preview folder. I'm going to assume it is here: "c:\stuff\stuff previews.lrdata"
The application is a console application, i.e. you run it from the command prompt, so you need to open a command prompt first. In the command prompt do this:
c:\users\yourname\downloads\DumpJPGs.exe "c:\stuff\stuff previews.lrdata" "c:\junk"
It should scroll by and do all the extracts it can. When it can't, it will skip the file and tell you. You should get a pike of output like this:
Wrote output file for c:\stuff\stuff Previews.lrdata\F\F8F6\F8F60553-DF8C-469C-8AE1-95632FE8CC40-65a72aa533bfc8f4d63600c2a4040288.lrprev as c:\junk\20170925-121923-F8F60553-DF8C-469C-8AE1-95632FE8CC40-65a72aa533bfc8f4d63600c2a4040288.jpg
The resulting file is a jpg you can look at with any image browser. The first part of the name is the date and time OF THE PREVIEW, that means it is likely the date/time of the last time you edited the photo. The file names are not known because this presumes you do not have a catalog. Worse, there's no metadata in these previews because Adobe does not copy the metadata into previews, so there is zero information available to help you, you have to look at each image and catalog it appropriately. The long letter part of the name relates to the preview filename -- it's not particularly useful though you can track back to that file if needed.
You can also run this against a small part of the preview folder just to see what it does, for example:
c:\users\yourname\downloads\DumpJPGs.exe "c:\stuff\stuff previews.lrdata\0\0C87" "c:\junk"
The extra \0\0C87 is one folder I found in my file, your names will be different. This would let you test, but you can just run them all and it should loop through thousands of files if needed (you need plenty of space in the output folder if so).
It's kind of quick and dirty, if you find bugs let me know I'll try to adjust.
It's 64 bit only, hopefully you are 64 bit. I don't have a 32 bit to test on, but can probably create code for it if really needed (honestly in today's hardware no one should be running 32 bit any more).
Stop struggling with Lightroom! There's no need to spend hours hunting for the answers to your Lightroom Classic questions. All the information you need is in 
