DC used to publish calendars in the 1970s, which were actually pretty cool -- each month had original art by professional artists (Jim Aparo, etc) that was very well done. Anyway, the 1976 calendar established characters' birthdays and dates for special events. You can find the entire list
at this site, but here are the Flashverse highlights:
Jan 13 - Birthday of Grodd the Super-Gorilla
Jan 16 - Birthday of Wally West (Kid Flash)
Jan 22 - Birthday of Roscoe Dillon (The Top)
Feb 18 - Birthday of Eobard Thawne Prof. Zoom (The Reverse Flash)
Mar 13 - Birthday of Mick Rory (Heat Wave)
Mar 19 - Birthday of Barry Allen (The Flash)
Mar 23 - Birthday of James Jesse (The Trickster)
Apr 3 - Birthday of Jay Garrick (Golden Age Flash)
Apr 19 - Birthday of Samuel Scudder (Mirror Master)
May 19 - Birthday of George "Digger" Harkness (Capt. Boomerang)
Jun 4 - Birthday of Mark Mardon (Weather Wizard)
Jun 22 - Birthday of Thomas Peterson (Pied Piper) [note: 'Thomas Peterson' was one of Piper's early aliases. It should be Hartley Rathaway, obviously.]
Jul 20 - Birthday of Al Desmond (Formerly Mr. Element and Dr. Alchemy)
Aug 16 - Birthday of Prof. Ira West The Flash's Father-In-Law
Sep 27 - Birthday of Iris Allen The Flash's Wife
Oct 23 - Freak Accident Gives Barry Allen Super-Speed. He Becomes The Flash.
Oct 30 - Birthday of Dexter Miles [sic] Curator of the Flash Museum
Nov 22 - Birthday of Abra Kadabra
Nov 24 - Barry & Iris Allen's Wedding Anniversary
Dec 11 - Birthday of Len Snart (Captain Cold)