[More information is never a bad thing, and this confirms what he was suspecting, but...]

Your past self? You did leave a letter addressed to her in that book. [not sorry about snooping through your bedroom!!!] But that could be another soul Rembrandt would claim since she is you, isn't that right? His contract never specified that he would only take one version of your soul, did it? Maybe he's free to take all of them.