I was only suggesting one, out of many scenarios.
It is not out of the realm of possibility that Apple sent out DTKs to certain select developers. How do you think that Microsoft had an ARM native Version of Office at WWDC? Could have the Microsoft Office developers been at Apple? Yes. Could they run their development software by remoting into an Apple AS system? Yes, they could. But just as likely as the above two scenarios is that Apple supplied some major developers with DTK units early. MAybe it was limited to large developers, maybe not. I can't say either way, but I don't think it is out of the realm of possibility that some developers got DTK kits early, and were not permitted to say anything through a strict NDA, just like Microsoft and Adobe didn't say anything.
As for the legal requirements, they too are unknown. The current DTK terms call for 12 months of use. The early DTK units could have had different terms (4 months, 6 months, 9 months, etc.) That it could have been 12 months is also possible, with Apple giving different terms to different developers as well. If, and I present this as only a possibility, not as a probability, Apple released the early DTKs in October of last year, then they would have needed to be returned in October of this year (assuming the current 12 month term was used for the early DTK units). It is likely that the AS Macs were supposed to be released this October, but, due to Covid-19, that the release date for the production AS Macs has slipped by a month or possibly more. While this slippage is understandable given the circumstances, the return date as originally specified in the early DTK agreement did not. So, the DTK units are still scheduled to be returned on the date of the agreement, it is only the production AS Macs that have slipped.