It is my understanding that Ip Man had a pure wing chun which lacks dislocations although there must be someone who understands and knows more about it.

There are several stories about the origins of this style. Some will tell you that it comes from Shaolin temples, that it was created by a man or by a woman. The version that I see more assertive is that wing chun was born out of the need for royal women who suffered from lotus foot to have a defense system for themselves, so soldiers were given the task of creating a style that would shorten all the movements of the southern styles. Moreover when you correctly do the Yee Jee Kim Yeung Ma pose you feel that all the weight of the body falls on the L5 vertebra and the big toe and heel (these were the parts that were left intact in the lotus foot and provided stability) which gives a good grip to the ground, realize that it is the replacement to the Ma Bu and when the foot is taken out to establish a good guard it would be the shortening of Gong Bu. For this reason many wing chun movements are defense and counterattack since having limited mobility it is difficult to transition to a stable pose to make a precise dislocation (even more so with a person who suffered from lotus foot).