As an example, it might happen that a scheduler turns a planned order into a production order several weeks or even months before production of that order starts. Or the forecast is worked by the MRP Run (and subsequently planned orders are generated) way beyond the short or even middle term.
At my current client, we have worked on a definition and rule set for planning, which I would like to share with you, so you may use it as a frame of reference if you find it useful.
Below graphic summarizes the concept and it must be said that there are two major rules valid in any planning system:
Rule of Planning #1: "There is a point in time after which planning activities end". This point in time is not today! It comes before today, exactly at the point where the frozen zone begins. Once you're in the frozen zone you are working with production orders. And production orders are supply elements that we are not planning with anymore. we're expediting on them, reschedule them, re-route operations to different work stations and react to exception messages they received from the MRP Run when actual results differ from the plan. If you find yourself looking for a tool to automatically re-assign and re-schedule within the frozen zone you either don't have a frozen zone or you're under the wrong assumption that the planning system should not only 'plan' but also fix deviations from the plan. These deviations are due to variability. And variability can only be buffered but not be planned. Especially not after it occurs.
Rule of Planning #2: "To plan your resources in the mid and long term level and manage demand - To plan your resources and sequence in the short term level, schedule and manage supply". It doesn't make sense to reshuffle planned orders in the long term. You shouldn't have any in the first place. In the long term you are working in SOP and therefore with a planning hierarchy, monthly demand figures and SOP orders that cause rough capacity requirements (and not detailed capacity requirements). In SOP you move the demand so that capacity violations are resolved. In the mid-term you should work with Long Term Planning (LTP) and its Planning Scenarios. A Planning Scenario contains a demand program which you can simulate (with simulated planned orders) for mid-term capacity planning. Here you should also work with the demand program until you find one that generates simulated planned orders which fit into your available capacity program. That is then the demand program (Planning Scenario) that you activate into the short term. Now you can run MRP on those Planned Independent Requirements and the resulting planned orders can be sequenced, leveled and scheduled in capacity planning. The latter activity was 'managing and scheduling supply' whereas the previous activities were concerned with 'leveling demand'