The thing that is "presumed to have been made during my period of employment" is "any _such_ invention, discovery or item of intellectual property", and the "su

The thing that is "presumed to have been made during my period of employment" is "any _such_ invention, discovery or item of intellectual property", and the "such" here refers to "each and every invention, discovery, (...) made (...) during my period of employment". It's pretty redundant and there could be a fight regarding when the invention was made vs disclosed, but the wording limits it to the period of employment.