If you are not changing the protein in the buffer for Ab incubations, you are fine. If you use just buffer without milk/ BSA and save/reuse the Ab dilution then the Ab solution will not last that long.
How important is it to titrate antibodies for human blood? I have done a lot of flow stainings in mouse cells, and always titrated abs. But with human cells, due to limited numbers of PBMCs, was wondering if I could just rely on what the company recommends. Also, I am doing stainings with much lower numbers of cells/tube (~25-50,000). Should I lower the Ab concentration? Any help of suggestions are greatly appreciated!