triviaink.com

I enjoyed the question and the search. I had to use some "strategy" to get the answer. HOWEVER "concurrent" is not the right word. The three series overlapped, but were not really concurrent.

Thanks about the question. But I don't think "concurrent" is all that strict, at least in general usage. It just means they happened at the same time--they don't have to have been exact contemporaries.

con·cur·rent   /kənˈkɜrənt, -ˈkʌr-/ Show Spelled[kuhn-kur-uhnt, -kuhr-] Show IPA
–adjective
1. occurring or existing simultaneously or side by side: concurrent attacks by land, sea, and air.
2. acting in conjunction; cooperating: the concurrent efforts of several legislators to pass the new law.
3. having equal authority or jurisdiction: two concurrent courts of law.
4. accordant or agreeing: concurrent testimony by three witnesses.
5. tending to or intersecting at the same point: four concurrent lines.