Can a soul that is normally freed from the Edo Tensei be resurrected again?
In order to answer your question, whether a freed soul from ET may be resurrected again or not, I will those points which has been aired on telly so far.

Yes, you can resurrect it.

Before I answer this question, you need to understand how ET works. For this, please refer here. Since you specifically said not to use any spoilers, you can visit the link which I shared.

For more proof, visit Edo Tensei wiki page. They did mention that:


  It is possible for a reincarnated shinobi to be revived into a real living body again. Madara, however, was resurrected without his original eyes, having died without them.