Sure, people can change their assessments in response to the changing circumstances. However, if the organization is open-ended, some people may leave, thus preserving their outdated assessment.
Indeed, if this value measurement is critical to the security of the system, this is a major security flaw. Simply, the subject being measured acts favourably for a while and then changes abruptly. If a lot of people have made their assessments beforehand, but aren't around to react to the change, then the attacker has free reign to do whatever he or she wants.
Therefore, make the measurement time sensitive. Use a time-decayed weight function, say, or an expiry.