When the SLAM process is done your water should be crystal clear, you should have no sign of green whatsoever, you will have a CC of .5 or less, and you will have passed an overnight chlorine test. I think the one you missed was the overnight test... you should SLAM again and until you meet all of the criteria, including overnight loss, and then you should be set to go.
If you have any nooks and crannies that algae can hide, lights, steps, etc, be sure to give them a good cleaning as well. It's also important to brush your pool walls and floor during the shock process as algae is good at hiding in any crevice it can find under debris or silt that might be there. I brush my floor often because we tend to get a lot of pollen and I want to be sure 1) it gets picked up by my filter, 2) it doesn't give algae a starting chance.
As far as where you get your chlorine... that shouldn't matter too much. If you're getting it from a store that doesn't have much business, they may have old stock, but otherwise you should be ok. You might find it is a little stronger at some places due to quick turnover of product, but that's a hard one to judge without testing before and shortly after the addition of the chlorine each time.