Need advice on partitioning W10 & recovering W8.1.

When I did a free upgrade from W8.1 to W10 the upgrade was corrupted, inasmuch as several default apps were missing, etc. I was in contact with MS on 4 occasions, 3 of them remotely operated my laptop, they attempted troubleshooting, scans, etc., but couldn't solve the problem. So with the 4th employee I decided that I wanted to return to W8.1. However, when he did the Settings>Update & Security>Recovery>Go back to Win8.1, the reply was: 'We're sorry but you can't go back. The files we need to take you back to a previous version of Windows were removed from this PC'. The MS guy tried to find out why but to no avail. He then suggested that he could do a reinstallation of Win10 by downloading & creating installation media on a USB flash drive. (at least 4GB needed). I inserted a clean flash drive & he went ahead & downloaded it. The next day I clicked on the setup.exe file in the flash drive folder & reinstalled Win10, everything went smoothly & a trouble-free W10 was installed. However, I noticed in the in File Explorer, in the Windows.old folder, (the Win8.1files) that the 'Recovery' file was empty. Is there anyway I can remedy that. MS says I can't but they would, wouldn't they! I would like to have a chance of installing Win8.1 along with Win10 on a partitioned C: drive. This has to be done before July 29 when the Windows.old folder will be deleted & no more free upgrades. Any suggestions please? Sorry this has been so long-winded!

July 29th has nothing to do with the Windows.old folder. What happens on July 29th is that new upgrades to Windows 10 will stop being free. You already have an upgrade, so for the computer that was upgraded you will continue to have the ability to upgrade to or re-install Windows 10 any time, as many times as you want on that same computer, even after July 29th.

It sounds like you did not make an image or backup of your Windows 8 before upgrading to Windows 10?

First thing to try is see if you can retrieve your Windows 8 product key:
https://www.tenforums.com/software-ap...7-showkey.html

Then get the Windows 8.1 ISO file to make install media from. Make sure to get the language and version of Windows 8.1 you had installed and your product key is good for:
Windows 8 ISO

Reinstall Windows 8.1, I would recommend you wipe the entire drive and do a clean install (boot from the install media, select the custom install option, delete every partition listed on the hard drive you are going to install to, with only unallocated space showing, click next to install to the unallocated space.) This will erase all of your programs and data so make sure you have a backup copy of anything you want to keep.

Now to dual boot Windows 10 and Windows 8, first you will need to purchase a full retail copy of Windows. You need two licenses for Windows to dual boot because it is two copies installed and activated at the same time. You currently only have your single license for Windows and an upgrade to Windows 10 does not create a second license - it uses the original license. Once you have two licenses for Windows then:

Shrink the current Windows 8 partition by however much you want to give to Windows 10. I recommend no less than 50 GB for either Windows 8 or Windows 10. You can do it in disk management, but I like MiniTool Partition Manager much better. Once you have the free space for Windows 10, create and format a primary NTFS partition for Windows 10 in the free space.
Best Free Partition Manager for Windows | MiniTool Partition Free

Create a Windows 10 installation media (or use the existing one that you have):
Windows 10

Boot from the Windows 10 installation media. Select custom install again. This time select the NTFS partition that you created and formatted for Windows 10 and install to that. It should set up dual booting with Windows 8.1 automatically.

NOTE: it looks like Windows downloads from Microsoft are not available (blank pages) at the moment. Probably because of the rollout of a new insider build, so if you get blank pages trying to download Windows, just keep trying. They should come back up in less than 1 day, I would hope.

Hi NavyLCDR,
First, thanks a lot for a very detailed & thorough explanation. The guy at MS did tell me that because I upgraded to W.10 on July 1, 2016, the Windows.old folder would be deleted 30 days later, & I would no longer be able to use the bootable flash drive to update to W.10 for free anymore, (I didn't understand that one!). It's going to take me a while to absorb all your advice, (I'm 83, & not so sharp anymore). No, I didn't make an image or do a backup before upgrading to W10. I just thought I would have the prerogative to go back to W.8.1 if I wanted to within the 30 days. I did backup all my personal files though. I don't understand why I would have to wipe the entire drive. The MS guy told me if I want to go back to W. 8.1 the only choice I'd have is to do a factory reset & that would do the trick, but of course that would put me right back to square one as if I'd just bought this Ultrabook laptop 18 months ago. That's why I wondered if I could make use of the Windows.old folder if I could resolve the issue with the empty 'Recovery' file! But if that's out I could still do a factory reset & go back to W. 8.1. The only thing that bothered me was that when I used the bootable flash drive to reinstall W.10, I didn't notice the choice of selecting the 'Custom' option, which would have allowed me to do a partition. Is that why you suggested I'd have to buy a new full retail copy?
By the way assuming your title is for real, I was in the Royal Navy & also the USNR (V) as an officer in San Diego. Thanks again.