Perhaps there is some archival material that could be used for Shatner's co-star Candice Bergen from when she was a little girl (including her appearance on 'You Bet Your Life' with Groucho!). And I suppose 'Brothers & Sisters' could recycle footage from 'Gidget' if they wanted a light-hearted lookback at Nora Walker's past, since Sally Field plays both roles.
And should the producers of 'Shark' ever need some 1970s flashbacks for Sebastian Stark, they could draw from the work of James Woods in such shows as 'Barnaby Jones', 'Police Story', 'Kojak', 'The Rookies', 'The Rockford Files', 'The Streets of San Francisco', and 'Bert D'Angelo, Superstar'. (His roles in 'Young Maverick' and "Holocaust" would be right out.....)
Otherwise, I think the gimmick would have to be reserved for special guest stars, and even then their body of work might only go back to the 1960s (which might seem not only "historical" but downright ancient to some viewers).
Off the top of my head, a list of such actors would include Peter Graves, Robert Culp, Robert Vaughn, Robert Conrad, Ed Asner, Sally Kellerman, George Grizzard, and Ephraim Zimbalist, Jr.
Think of how many TV programs they could utilize for flashbacks of a character played by Leslie Nielsen!
The producers of 'NCIS' could also create plenty of flashbacks for Secretary of the Navy (formerly Senator) Edward Sheffield from all of the early work by Dean Stockwell. Stockwell played Sheffield on 'First Monday' and 'JAG' (from which 'NCIS' was spun off).
The show that should look into using this ploy is 'Cold Case' on CBS. However, they've done a pretty good job so far of matching up actors to play the younger and older versions of characters. But why not do an episode in which retired NYPD Detective Adam Flint (Paul Burke of 'Naked City') has an unsolved case that he can't let go, and it takes him to Philadelphia?
Of course, he'd never have to leave the Big Apple if such a case could be worked into a plot for 'CSI: NY' or 'Without A Trace'. Since 'Naked City' was an ABC production, the gimmick could have been kept in-house had it been employed by 'NYPD Blue' when they had the chance.
According to the IMDb.com, Mr. Burke has retired from acting. But at least he went out on top - with a guest stint on one of the better ABC 'Columbo' episodes, "Uneasy Lies The Crown".
I've posted in the past, going all the way back to the old "Tubeworld Dynamic" website, that someday - while Frank Converse is still among us! - 'Coronet Blue' should be given some kind of video resolution so that we in the audience could finally learn what those words meant and who Converse's character really was. (You can find Larry Cohen's splainin online as to how he envisioned the ending, but it's not the same thing as seeing it played out on the TV screen.)
At the time I first wrote about it, I saw 'Diagnosis Murder' as the type of show that could wrap up the 'Coronet Blue' storyline. Since then, 'Without A Trace' and 'CSI: NY', maybe 'Law & Order: Criminal Intent', are probably the best candidates today. (Even 'Blind Justice' could have tackled it!)