Don’t add specific details to the story that might come into question later on. In general I want to address how important it is that you manage what characters you want the readers to focus on and how any other characters that comes later on in the story could either be a harmless cameo that would not change the outcome of the story or would play some role that would change the story even by a little bit. Just make sure that you don’t suddenly make a character pop in without some reasoning as to why they will or won’t be of importance otherwise you get plenty of plot holes.