"has remained until now" is correct and usable in written English.
You can use it when referring to something that has not changed, or persists, over a period of time. For example, "The tradition of celebrating Thanksgiving in the United States has remained until now."
Beyond the haze of elaborately revised fictions from both the political left and the political right is a bizarre account that has remained, until now, the great untold story of modern Texas politics.
In this article I use this model to investigate an area of geographic study that has remained until now unexamined under this lens: the production of heritage landscapes.
However, the real dynamics of extragenetic acquired resistance in a growing population of cancer cells has remained, until now, unknown.
And although since then election campaigns have generated a cascade of words on the prospects of the centre party and speculation about the possibilities of a hung parliament, those have remained until now just that – speculation – to be set aside as soon as the votes were counted and the usual politics of two-party government-and-opposition could resume.
Only its precise location has remained secret, until now.
But the rest of the union's proposal has remained confidential until now.
The army has remained neutral until now, but its restraint may not last.
The British version of events, written less than 48 hours after the attack in 2012, has remained secret until now.
By Richard Brody The celebrated comedian Bert Williams stars in a 1913 film that has remained unseen until now.
"The degree to which the U.S.A. knew about and supported these operations has remained secret until now," he said.
The hormone, which stimulates the growth of muscles and bones, was added to the International Olympic Committee's list of banned substances in 1989 and has remained undetectable until now.
