I bid for partial month COLA’s several times in the past as a 756 FO in DCA. Each time I was denied the COLA because it went senior to me.
I also usually bid reserve in the winter as we were rarely used. It was great for checking things off the to do list, as long as they were the type of thing that could be done whenever, not time critical. I don’t commute - if I did, I wouldn’t voluntarily bid reserve. Nor would I bid reserve in busy months.