Say that I'd recently purchased 10 PCs from a retailer, but ordered them without any OEM operating systems, am I then at a later date allowed to go back to the same retailer and purchase 10 copies of OEM Windows, and legally install them on those PCs, or can I only legally use OEM copies of Windows that were purchased at the same time as the computer?
I would have thought I couldn't do this after the event, but if that is the case, why do many retailers (including big companies such as Dell) allow consumers to purchase OEM copies of Windows via their website without purchasing any hardware at the same time?
If there are any constraints, (e.g. you only have a limited time in which you can do this), what are they?
Edit: Additional Background Info (although, this makes the question more suitable for SF now)...
I'm about to enter a Microsoft Open Value Licensing Agreement, but all the OS licenses available under OVL are upgrade only. So I either go back to the supplier (Dell, as it happens) and purchase OEM copies, or I purchase the cheapest retail OS I can find that I can legally upgrade to Windows 7 Pro. I expect I can get OEM copies cheaper, but I need to ensure that whatever option I choose, that the business is license compliant.