In "Cambridge preparation to TOEFL"'93 book I've found the phrase:
_ untold number of people perished while attempting to cross Death Valley.
The correct answer is "an". But I have that feeling that "the untold number" = "the specific number, i.e. 12345 that was not told". So the article should or could be "the".
If there is any difference, tell me the British version of this.