When did block release training or work experience start getting called co-op given that in various areas of the world a coop co-op means a cooperative like Mondragon.

I have only seen it (co-op) used in the last few years.

Well I finished school longer than a few years ago and cooperative education (co-op for short) has been around since the early 20th century.

http://www.ceiainc.org/history

http://en.wikipedia.org/wiki/Cooperative_education