From the QI website:
I have to declare an interest here, since the fact of there being 21 times as many words which break the "rule" as obey it came from me. (Using a Scrabble word list, and with technical help from my stepdaughter and from Davini994, who used to be a regular on these forums.)
And what we found was 923 words which have <cie>, 2,606 words which have <ei> after something other than <c>, and just 167 words which really do have <cei>. (Of which only six are really in everyday use.)Regards
Barry