hi there,
for what I've read, and believe me I know because I'm having issues regarding this, you must get it! fight for it! knock every door, call everyone and see who can give you that letter. That letter is the key to the residence.
You might prove your work period, salary, and hours with the Record of Employment, but your activities must be state in that latter. And even doing this, your case would be like flipping a coin in the air.
The bottom line is the more you can get in that letter the better.