I agree. This letter can NEVER be signed by the secretary of your department. A lot (and I repeat, A LOT) of early (2011) applicants had their applications returned because they made this mistake. Better have this letter signed directly by the graduate studies office then have it returned later. And PhD stream may not even exist anymore, so do it now and do it without making any costly mistakes.
I think the important thing here is that, within the last ten years, you need at least one year of full-time (or equivalent) continuous work experience in one occupation only (provided it's skill level A, B or O). Let's say you have six months in job A, and six months in job B, then the work experience won't be accepted to satisfy the minimum requirements of one year of continuous work experience (it will still be accepted for point calculation, but not to satisfy minimum requirements).
For example, let's say you work on three different places
You work 6 months in job A
You work 7 months in job B
and 8 months in job C
Then you would NOT satisfy the minimum requirements and your application will be rejected, even though in total, you have more than one year of work experience.
But let's say you work 13 continuous months in job A,
7 months in job B
and 8 months in job C
Then you will satisfy the minimum work experience requirements, and at the same time, you can add the non-continuous 7 and 8 month periods to contribute to your total work experience (which will be in total 28 months).
That's my interpretation of the rule, I don't know if it has been changed, or if I have made a mistake in my interpretation.
As for CEC, I think they have made it explicit that the work experience does not have to be continuous,