I'm have been trying to annotate some RNAseq data using the org.Mm.eg.db. The count matrix I was sent by collaborators has ENSEMBL gene IDs. However, I have been having a problem with missing gene ids in the egENSEMBL table when I try to annotate. For example, one gene I am interested in, H19, has the gene_id 14955, but this id does not seem to be present in egENSEMBL. On the other hand 14955 is present in egSYMBOL. Is there something basic I am missing? Is there a different table I should be using?