Covenant technology

Broadly speaking, there are three classes of Covenant technology:

Entrusted technology is understood and produced only by High Charity. There is a simple and ironclad line of dogma to justify this: Since the Prophets are entrusted with the search for the Great Journey, they are also entrusted with the disposal of the technology discovered in that search. The Prophets have the final say one what technology the Holy Ecumene is properly prepared to receive, and what technology must remain restricted to the higher castes, though it must be noted that their say has sometimes been swayed by very persuasive civil wars.
 * Entrusted technology

Some entrusted technologies are passed out to clans and secular governments outside of the Ministries, although manufacturing and maintenance has always remained under the control of the Prophets. But when the Prophets deem that the time has come, the trust is expanded to the entire Holy Ecumene, or at least the parts in good standing. This is sanctioned technology, which may be manufactured or repaired with the blessing of High Charity.
 * Sanctioned technology

Some entrusted technology become sanctioned within a generation of its discovery, while other forms of technology will only be sanctioned long after it is obsolete. Slipspace drives are one such example. The slipspace drives available on the open market are only a few generations more advanced than the ones that the Sangheili developed natively.

Native technology is the technological and industrial base that each client race brings to the Covenant. Whether medicine or rocket technology or computer science, this technology remains in use for a long time after the species’ incorporation into the Covenant. Officially, there is nothing wrong with using the tools that you have developed before the light of High Charity graced your doorstep, as long as those tools did not violate Covenant dogma (e.g. Associated Intelligences). Unofficially, the Ministries drown each new client species in a metaphorical deluge of technological gifts until the metaphorical bubbles from native industry stop.
 * Native technology

So. Do the Covenant understand their own technology? It depends. There exist many guilds whose members have a functional understanding of sanctioned technology and its manufacture. Entrusted technology is considerably rarer, and wasn't fully understood even by the Prophets. Outside the lost Ministries, its study and maintenance was carried out in secret by wealthy clans and underworld organizations. Entrusted technology can be had in the post-war world, for the right price, from the right friends.

With the Covenant, it is also important to be mindful of the distinction between them understanding their technology and being able to operate it. The Covenant's understanding of their technology was ritualistic and surface-level: their machinists did have a decent understanding of the specific procedures required to operate or even repair the technologies entrusted to them, but this did not mean they understood the principles governing their inner workings. As such, without the Prophets, the ex-Covenant at large still retain a fair bit of know-how on how to repair, even manufacture their existing technology; however, the ability to innovate and create new technologies, or apply existing technologies in novel ways, are rare and treasured talents.

Though they were distributed to the domains, entrusted-grade assembly forges and fabricaries were mostly black boxes, and required highly specific incantations and rites to operate. Most pointedly, they could only be maintained or replaced with personnel and tools from the Ministries.