Now that phrase, "on certain occasions, " carries no phrase of frequently or numerosity.

CNN

"In their letters, there is a lot of emotion and, on certain occasions, a lot of humour, " she said.

BBC: Portrait of Emily Gair Greg and her father's letter

Clinton would wear the small, undetectable hearing aids in each ear only on certain occasions, such as in crowds, his doctor said.

CNN: Clinton Gets A Hearing Aid, Loses A Cyst

Assuming that the majority is correct in it's assumption that there are 11 or 17, can anyone imagine a trial in this court or in any other court in which the issue of whether certain occasions by definition could not mean 17 and occasionally could not refer to 11 would be the issue being litigated?

CNN: Transcript: White House Counsel Ruff's opening statement

America did not abolish the business cycle in the 1920s or the 1960s, nor did Japan in the 1980s, though many were certain of the fact on all three occasions.

ECONOMIST: Beyond the business cycle?

He has been dropped and recalled on 10 occasions, but rival Michael Vaughan now appears certain to start the summer in the England side, providing he does not have any injury problems.

BBC: Graeme Hick batting against Sri Lanka

Leinster wasted try-scoring chances either side of the interval with prop Cian Healy spilling the ball on two crucial occasions and Contepomi's forward pass preventing a certain Luke Fitzgerald touchdown.

BBC: Leinster 12-3 Edinburgh