To add to Mary's great answer, there is a field on each track's description page called "Data last updated:" that may be helpful for those wanting update information directly from the Genome Browser [GB] or database tables.
To web browse/extract this update tag in the GB, and example would be:
[?]- UCSC browser
[?]- select "Human Feb. 2009 (GRCh37/hg19)" aka hg19
[?]- on the assembly browser page, click on any track name
[?]- in the top section, bottom field is "Data last updated:"
Please note that for composite tracks you will need to click into one of the sub-tracks to view the update date, as each is independently created/updated.
A way to retrieve the data in a table/file format is to use the Table Browser [TB] (or direct FTP, or the public mySQL database) and navigate to the database.table == hgFixed.trackVersion. The database, track name, update time, etc. is all there.
The path in the TB is a bit different than a regular database query:
[?]- start with any database
[?]- select group: all tables, database: hgFixed, and table: hgFixed.trackVersion
[?]- download the table
Hopefully this is helpful!