I can't find them either. In answer to your question about whether the census is complete or not - we can never know if any historical records really are complete. I know from personal experience how many of my friends have been missed off census counting in recent years, so I am sure that has always happened. Also, we rely mostly on transcripts - first the enumerator makes their notes, then they transfer them to a record book, which gets copied and someone has to transcribe - heaps of opportunity for mistakes to be made, names to be copied wrongly, whole pages to be missed off, etc. Add to that the fact that sometimes even the official records go missing or get destroyed. I did check if there were any known issues with the 1881 census (i.e. obviously missing volumes that had been reporte) and there didn't appear to be, but that still doesn't mean that it is complete.
You may end up finding them at some point. Someone might come across a really bad transcript and submit corrections and suddenly you will be able to find them in the indexes. I know I have been doing that for SENNETTs - there have been some that would have been impossible to find before, the way they were indexed, but I have had them corrected.