The original is what was REVEALED, and has been committed to memory in a continuous living chain of transmitters from that time to this. Even if ALL copies were destroyed, this original can be reconstituted from memory by Muslims in any part of the world, for there are memorizers (Huffaaz)wherever there are Muslims, even in the US! Something that is impossible with the Bible, whose original is lost.
The Koran that Muslims believe is the original one was compiled by Caliph Uthman who set up a committee to do it in 651 AD by using a method known today as "cut and paste". After the remnants of the old Korans were discovered in the Yemen's Grand Mosque, we now have an indisputable proof that the Uthman's Koran was only the latest version. That of course, means that Muslim belief in the Koran being an "unchanged word of God" is, to put it mildly, baseless.