The -I switch does not use the iteration numbers, it suppresses the output of .node file, so your input file won't be overwritten. It cannot be used with the -r switch, because that would overwrite your input .ele file. It shouldn't be used with the -q, -a, -s, or -t switch if you are using a .node file for input, because no .node file is written, so there is no record of any added Steiner points.