The majority of those seem to be TrEMBL, unreviewed (computer annotated) entries from UniProtKB and could explain the absence of results from Reactome. O70209, Q91YJ3, Q91YJ5, Q8BM55 seem to be reviewed though. See more about those statuses here. It seems Reactome is human centric, so perhaps the above SW entries from mouse are still to be inferred from the human pathway counterparts? Human TrEMBL does not return any results in BioMart .e.g Q9NQR3 and Q15505. It may be a good idea to contact Reactome for a definitive answer.