Years ago ,when I worked on elections, I remember the local Returning Officer commenting that a high percentage of special votes were not allowed or wasted. I don't remember hearing why this was so but the message we were getting behind the desks was that anyone who came in to vote and was not on the register was to be given a special vote, no argument, and its validity would be decided at the count. This "validity" question may well be behind the long delay between the election and the final count