This actually does not really matter. As long as all the images contain the information of what colour profile they used, AND you have enabled PM's colour management (afaik, on by default), you should be fine and PM will show you the right preview. Even if some of your images are still sRGB, aRGB, or whatever. The colour profile you can set within PM is only used whenever PM can not find the profile information within your file.
Does this explain things a bit?