There are two ways to "loose" a formula that spring to mind:
1) a conflict arose and the knowledge and databses including backups were destroyed
2) someone made the knowledge disappear, because of reasons of his own.
What happened in the 2800 elite timeline?
Here some excerpts:
2350s Sirius corporation founded, grows rich supplying the war fleets.
2900 inferred After a series of peace talks, the Empire and Federation decide to form a special joint task force whose "official" purpose is research and development of spacecraft and space living technology. It is given the name Intergalactic Naval Research Arm, or INRA for short.
3050 inferred First reported contact with insectoid alien race known as the Thargoids ends in hostility.
3055 inferred The Thargoid invasion officially begins. Massive fleets of Thargoid warships carrying remote controlled fighters ruthlessly cut a swathe into occupied human territory, encroaching on a cluster of stars centred around Alioth. GalCop Navy is mobilized to respond.
Source:
Elite Wiki Alioth
No direct mention of the "quirium drives" in the source or any other.
This must be "new lore" added as some kind of a hint.
Alioth wiki article about "quirium":
http://wiki.alioth.net/index.php/Quirium
Excerpt from the article mentioning thargoids and DISO system:
"In late 2850 a damaged Thargoid ship was captured and made available to GalCop researchers who found a largely intact power system. Two teams were assigned to work on the new technology, one highly secret, from the military research arm, and another more public, led by Dr. Quirahn Falayn, a native of Diso."