What is meant by "a little bit different"? When I worked with bulk colchicine the major issue was to avoid light exposure; otherwise it was stored at room temperature. By storing the material at -20C you risk condensing water into the material if it was opened while it was still cold, this may cause a reduction in activity if this is what you mean by "a little bit different". If the material was exposed to light it could contain significant amounts of Lumicolchicine which can be detected by TLC on silica gel plates developed in ethylacetate:methanol (9:1), colchicine stays near the origin while the lumicolchicines elutes near the middle of the plate.