The novels of Dickens are full of coincidences, and one of the great abilities of Dickens is his ability to make us as readers believe in them and not to think that he has stretched the realms of possibility too far.
The third stage contains a number of "revelations" that "wrap up" the novel and make it a very neat ending. The first coincidence comes after Magwitch has shared his tale and Herbert identifies Compeyson as the man who jilted Miss Havisham all those years ago and set her on her path to gain revenge on all men through Estella. The sinister figure of Compeyson cropping up again during Wopsle´s pantomime again shows that he is a figure from the past who haunts the action.
The second coincidence concerns the true identity of Molly, Jaggers´ housekeeper, as the mother of Estella. This truth is further developed in Chapter 50 when Pip learns that Estella is Magwitch´s daughter. This cements the link between money and great expectations and crime in the novel. To Pip, to find out that his long-cherished dream of marrying Estella (symbolic of "Great Expectations") would only further link him to crime is a big shock. It appears all wealth has its roots in crime - a key theme in the novel.
So, the last stage contains many coincidences that are hinted at throughout the novel. The question for us a readers is are they credible coincidences or is Dickens stretching things too far.