The phrase "added still further" is correct and usable in written English.
It can be used to indicate that something has been increased or supplemented beyond what was previously mentioned.
Example: "The report was comprehensive, but the researcher added still further details to enhance its clarity."
Alternatives: "added even more" or "further supplemented".
The tests were condemned by American and Israeli officials, adding still further to the tension between Iran and the West over Iran's nuclear ambitions.
Age determinations also can now be made of low-uranium trace minerals such as rutile (TiO2), a common constituent found in mineral deposits, adding still further to the number of entities that are datable by the uranium lead method.
This skywriting adds still further to the romantic reputation of the young officer, so that when he announces that he is holding a photographic exhibition in his apartment, influential figures from the armed forces and Chilean high society show up for the opening.
All of this adds still further to a personal legacy that as long ago as 2000 was sufficient to have Warne named by Wisden Cricketers' Almanack, the game's venerable annual record, as one of its Five Cricketers of the Twentieth Century.
Propagation and development of these standards, together with training in basic informatics for pathologists, would add still further to the efficiency and usefulness of the approach.
But this adds still a further complication, for the Principia itself was substantially different things to different people.
And they add yet further that they are still waiting for Britain to say exactly what changes it would like to make in the treaties of the European Union.
The risk, though, is that the threat of Islamic militancy helps to defocus the alliance further, adding still more tasks to its "to do" list, reducing consensus about where the greatest danger lies and the costs involved in addressing it.
During his speech, Mr Cameron also said the UK was working with internet firms on the issue of removing extremist online material - but added there was still "further to go".
The CAP is devoted to expanding this still further, adding more lakefront parkland and boating space (Chicago already has the country's largest harbour system), and even creating offshore islands to attract birds and tourists.But Mr Daley has been tidying up the inner-city too.
