I don't add new pollen to old pollen, I just have several vials/matchboxes of the same pollen. If I end up with too many I throw out the older ones. Once in a while I will combine them into one container but I do it in the freezer without taking them out into room temperature.
In my experience, thawing and refreezing pollen does not make it non-viable. We take pollen out and use it sometimes daily then put it right back in the freezer. I have some pollen that's a year old that was used last season and then I kept and used this season.
I use a lot of frozen pollen in the beginning of the season when the new ones I'm wanting to use have not bloomed yet. Another reason I use frozen pollen is because some days I am out pollinating before the anthers are open and the pollen is ready. Sometimes I just don't have time, especially when the mornings were cooler, to wait until all the pollen is ready. I try and use a limited number of pollen parents so sometimes they aren't blooming when I need them.
