ffmpeg "Stream specifier matches no streams", but it exists
For future reference:

as specified, you cannot reuse an intermediate stream more than once so you have 2 options:


either save it, input the saved file and reuse it as many times you need in your filter;



  ffmpeg -i file1 -i file2 -i savedStream -filter_complex "..."



use the split filter and create as many outputs you need; default value for split is 2 outputs so:



  [o0]split[split1][split2]


would be your case.