I was just about to write a response to your scenarios 1 and 2 and realised there are three ways I can think of to get the " right " answers.
As you pointed out many FA's dont understand their payslips but its got nothing to do with earnings but rather apathy.
I would pick up the phone to ask operations first and if not satisfied with that then call the FAAA. As tedious as it is to wade through the EBA document the answers are probably in there too.
If you have a duty cancelled then you will be pay protected for the same number of hours which can be recovered by assigning you a duty on A days. I dont know if QCCA crew can decline an assigned duty and drop the pay protection but a phone call to ops will clarify that.
Overtime from a specific bid period is usually paid on day 29 ( 2nd Pay day ) of the next bid period.
A lot of crew view operations as the enemy but if you are polite in your phone manner then 99% of the time they are very helpful.