Well, I didn't say sigma is wrong. A recommendation such as "store in fridge" is fine and quite sufficient for practical purposes. Sigma does not say "DO NOT FREEZE", which means that they have not really assayed the effect of freezing on the product.

SWIM once ordered an antibody from another big player company, its MSDS said "DO NOT FREEZE" so he called the company and he asked them what would actually happen if he does freeze it. They said that it won't hurt, even thought repeated freeze-thaw cycles will damage the product. The customer services actually recommended freezing the antibody in aliquots, so a "single dose" can be thawed and used without compromising of the total product.

And they were actually right. This product still frozen is still working for SWIM after 4 years. The MSDS was stating the expiry date is one year after purchase, recommended storage in the fridge.

Basically what I am trying to say is that MSDS are not be believed as a holy text or something. They do contain useful information but there are much more to these.