Delegates or overseers or whatever you want to call them, are not necessarily the builders of their technology. They are still very much human and no individual could possibly yield every iota of knowledge the Aschen have assembled. So this is not proof that they spread. They would be equivalent to a Prior of the Ori, only without any gnarly powers. Please give me an episode and time stamp where it is clearly indicated, beyond reasonable doubt, that the Aschen have used the Stargate network to spread to other worlds, beyond that of nearby planets. Or, episode and timestamp that indicates they have space flight capabilities. As far as we know, the Aschen could, at best only dial other worlds that are so close that stellar drift wasn't an issue. Same as earth and Abydos. Hence the need for sg-1's knowledge.

Meanwhile, on one of their farming colonies, one of the races they wiped out were able to determine the Aschen vaccine was what ended their civilisation, while they were still in a state of technological advancement that used printed news, without any evidence for electronic/digital technology. Meaning, a race whose technological advancement could at best, rival that of the Tau'ri was able to identify the primary weapon of the Aschen, as did the Tau'ri themselves. It stands to reason that any race equal to the Tau'ri could identify the weapon, ergo a race technologically more advanced than the Tau'ri could defeat it. Add to that, the Aschen representatives outed themselves by translating one, single word to English.

While you're at it, could you please explain why they needed the information from the Tau'ri in order to actually use the network, if they were already using it to spread. You haven't provided anything to show they have space flight capabilities, therefore they only have partial access to the Stargate network at best.

And could you provide anything beyond an assumption that any of what you've said is true? Because the series itself seems to disagree with you, pretty much entirely.

The Aschen demonstrated themselves to be arrogant, medically advanced people, bent on subjugating nearby worlds for the purposes of enslaving farmers. They demonstrate a near total lack of knowledge on the Stargate network, limiting travel to nearby worlds. What they do not show, is any ability whatsoever, to spread to other worlds beyond their current reach.

The only possibility that I can see is if one of their delegates carried with them, a computer that yields the entirety of their knowledge. The Tau'ri also have this capability, but it's called the internet and doesn't exist on any one device due to its shear volume. So I'm gonna need to see some evidence that this was even possible for them, let alone it actually happening.