Looks like you hoarded your 50 "full retail keys" for nothing then. Of course, if they were in fact "full retail keys" you could sell the licenses; but since they're OEM-sourced that's obviously not the case.
The free upgrade offer is based on the hardware of the upgrading activated system, not a key. So, no. You can't use your 50 win7 keys to get 50 win10 keys.
This is what happens when you listen to someone at Microcenter. That's your first mistake. There's no such thing as a pre-activated ISO of Windows 10 that you can download -- well, not legally anyway. Any pre-activated ISO that you might find would use some sort of patch (such as the DAZ Loader for Win7) and it wouldn't use any of your keys. Activation of Windows 10 using the free Win7 --> Win10 upgrade is tied to the Hardware ID of the computer you install Win10 on. If you only have one computer then those 50 keys are useless.
If they are indeed retail keys (and not OEM), then the licence carries the entitlement to be installed on any machine, and later moved to a different machine. This licence entitlement is retained even if you upgrade to Windows 10 using the free upgrade program. When doing a fresh installation of Windows 10 November Update (build 10586) or later, you should be able to enter a Windows 7 retail key to activate. Combining the two facts above, you could do this on a single PC: install Windows 10, activate with a Windows 7 key, wipe, reinstall, activate with another Windows 7 key and so on. You would then have the licence entitlement to several copies of Windows 10, which later you are entitled to move to a different machine. Do note that the above gives you a licencing, and not a technical entitlement. In practice, because of the hardware-bound nature of Windows 10 activations, you may have difficulties moving Windows 10 to different machines. However, as you are licenced to do so, you will be able to talk to Microsoft who will help with the moves. Do note that the above does not apply if your keys are in fact OEM upgrade keys.
I didn't forget. I never suggested that Windows 7 keys would work after 29 July. The OP would have to install Windows 10 50 times now, in order to get the upgrade licence entitlements. Once that's done, the Windows 7 keys are not needed anymore. To summarise: install Windows 10 now using Windows 7 key, get activated, get the entitlement to Windows 10 licence. In the future, when you actually want to use it, move Windows 10 to whatever machine you want to use it on. You will be licenced and entitled to do so.
How do you do that when each installation is activated based on certain pieces of hardware? i.e. Hardware ID and if the hardware changes enough, activation fails. What am I missing here?
1: he doesnt have the machines to activate the HWID on MS servers.. transfer what ? hdd ? a key you dont have and if you do u cant move to a new pc as its HWID is different.
Come on guys, lets keep him happy, let him move what he does not have in exchange for something that does not exist, and then it will all be different. I hope that makes sense...
Guys/girls, if you want to transfer License (if you have existing retail key you upgraded with) you need to contact support, you will be able to transfer though OP might have a bit of a problem if he wants to transfer 50x licenses, don't think support will play along. We don't know yet if Microsoft plans to keep already-upgraded W7/W8 keys working to activate W10 after July 29th, that's a mystery for now.
Upgrade all 50 copies on the same machine. I'd imagine he has at least one machine, but even a single Virtual Machine will do. Transfer the software. That is a licencing concern, not a technical one. You do not have to be able to transfer anything tangible such as an hdd or a product key. Although a product key can represent the right to a licence, a product key does not equal a licence. I am sure people remember the days when product keys didn't exist yet, but the concept of a licence was very much in use. Even without a product key, you can very much specify in the licence terms that a piece of software is installed on one machine only. To move it, you'd uninstall on one machine and install on another. This is a licencing issue, not a technical one.