Unless you have only one reoccurring character in your novel there is a very good chance that somewhere you made a mistake where they are concerned. I have a few tricks I use to help me keep track of every character detail so I don't accidentally change an eye color, age, or something else. The first thing I do is start a notebook at the outlining stages of my novel. I jot down every main and supporting characters description, birth dates, any habits, catch phrases, or quirks of their personality. This helps reduce the amount of errors I have to look for when it comes time to edit.
Once the novel is finished I get a different colored highlighter for each of my reoccurring characters. I go through and highlight every time they appear in the novel, whether it is dialogue, action, or just an appearance. Then I cross reference with my description in my notebook and make sure I haven't made any mistakes. I almost always do.
After that I take note of how often a character showed up in the novel and what type of scene it was, tension, action, or development. Sometimes I find that I have to add scenes because I didn't develop an important character enough. Sometimes this reveals that a character is unnecessary and it results in having to cut them from the novel. The end result is not only stronger characters, but a stronger novel as well.
Whatever method you use, just be sure that you are checking your character details to make sure they stayed consistent throughout the novel. I once ended up with a character with two different colored eyes. It was not on purpose. Worse, I almost sent a partial of it out! Don't let this happen to you!