For RefSeq genes, see this discussion: https://groups.google.com/a/soe.ucsc.edu/forum/#!topic/genome/ClmwZbanI_g/discussion
Vega: Look in hgFixed.trackVersion or click on a Vega gene in the Genome Browser. (Note that Vega is actually a subset of Ensembl and Gencode (Gencode is human only) that is manually annotated. They should state somewhere on their site which version of Vega is equal to which version of the other dbs: http://vega.sanger.ac.uk/index.html)
Ensembl: Look in hgFixed.trackVersion or view the track description in the Genome Browser.
CCDS: These are updated, I believe, once every 6 months by us. I
don't think we store a version number for this one, but if you go
to the track description page, we do list the date it was last
updated. (Note, on the track description page it says, "CDS
annotations of the human genome were obtained from two sources:
NCBI RefSeq and a union of the gene annotations from Ensembl and
Vega, collectively known as Hinxton.")
For any other ones that you may not have mentioned, the best
place to start is on the track description page.
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