Hi Brian, There is quite a bit of knowledge floating around on this subject. Unfortunately I think you will find it is really Ab dependent so there are no hard and fast rules. In addition one needs to rule out many variables (provide more detail on storage) before arriving at a root cause. Sev. examples; the rate of freezing and the head space and surface vol. matter. Can you guarantee it hasn't gone through any freeze-thaw cycles, is the pI close enough to the pH that upon freezing the change in pH has caused precipitation, any analytical (SEC, gel, etc) tests performed to ensure an intact and competent molecule at the correct concentration still exists in the vial. On and on. As an example of generic shelf life most commercial sites list 24 months as the shelf life. Also the functional assay used matters. In my experience, WB is not sensitive to slight conformational changes as other assays. Here are sev. good lit. refs. I have a ton more if interested. https://www.labome.com/method/Antibody-Shelf-Life-How-to-Store-Antibodies.html Biotechnol Prog. 2010 May-Jun;26(3):727-33. doi: 10.1002/btpr.377. Impact of freezing on pH of buffered solutions and consequences for monoclonal antibody aggregation. Kolhe P1, Amend E, Singh SK. J Histochem Cytochem. 1983 May;31(5):691-6. Monoclonal antibody storage conditions, and concentration effects on immunohistochemical specificity. Ciocca DR, Adams DJ, Bjercke RJ, Sledge GW Jr, Edwards DP, Chamness GC, McGuire WL. Pharm Res. 2013 Apr;30(4):968-84. doi: 10.1007/s11095-012-0933-z. Epub 2012 Nov 27. Effect of pH and excipients on structure, dynamics, and long-term stability of a model IgG1 monoclonal antibody upon freeze-drying. Park J1, Nagapudi K, Vergara C, Ramachander R, Laurence JS, Krishnan S. Pharm Res. 2011 Apr;28(4):873-85. doi: 10.1007/s11095-010-0343-z. Epub 2011 Jan 7. Frozen state storage instability of a monoclonal antibody: aggregation as a consequence of trehalose crystallization and protein unfolding. Singh SK1, Kolhe P, Mehta AP, Chico SC, Lary AL, Huang M.