What does uniprot consider "unambiguous" evidence for the subcellular domain of a protein?
Following your question, we have updated the documentation for topological domains in UniProtKB:
http://www.uniprot.org/help/topo_dom

I hope you will find it more informative now. Please don't hesitate to contact the UniProt helpdesk if you have any additional questions (or, if you prefer to discuss here, a short note to the helpdesk would help us spot your posting more reliably, since we cannot closely monitor all forums as you may understand).