While working at previous employers I have been exposed to confidential technical information. As usual, this is covered in the confidentiality agreement that I signed. The agreement puts no expiration date on this, i.e. it says something like "during your employment and any time thereafter".
Now in many cases, this information is quite old, i.e. 10+ years and I have no way of knowing whether the company would still consider it confidential, uses is or is even aware of it's existence any more.
Technical knowledge in general progresses fast so there is some "time value" on it: the older it gets, the less relevant and confidential it will be.
Is there a reasonable expectation of when the confidentiality requirement for for general technical information expires? It's not patented or protected in any other formal way.