GAO is Wrong

• You keep the necessary records in the baseline schedule, no need to clutter the schedule; nothing is ever lost but kept in their proper database location.
• At some point the activities must be actualized with some progress, otherwise retained logic will distort the schedule beyond comprehension.
• In a properly developed CPM schedule all activities are part of a chain even if start-activity-finish.
• It is as easy as 1-2-3 to prevent duplicating activity ID’s by simply adding a unique prefix/suffix to new activities for every schedule revision.
• If the data is stored on baseline table auditing is no issue.
• Do you mean P6 cannot compare activities existing on different updates if activities are deleted?  If so then transfer the data to a better designed database. Even Excel can make it.
• Not all CPM software is so poorly designed.
• Keeping deleted activities as milestones will make project statistics useless, number of activities will distort the statistics.
• How many rules and exceptions are you going to suggest?
• There are too many fields related of activity records that can distort the schedule that the only safe way to prevent the milestone to impact the schedule is to delete them.

I do not trust GAO as to suggest anything.  Unfortunately many will copy-cat GAO and some will go to the extreme as to declare it a standard to be strictly followed as a contract requirement.

In next reference, figure black bars belong to COMPARISON schedule; Termite Treatment has only black bar and data for comparison schedule. Termite Treatment has no current schedule data, otherwise would be misleading.

GAO got most of its preaching about lag wrong, very wrong: When GAO claims there is no effort or resources are associated with lag they are misleading the scheduler. They are not aware of volume lag concept and preach their old fashioned theories based on 1960’s CPM models.

GAO is right with regard to time lag that represents the elapse of time. Time lag happens when the elapse of time is independent of predecessor activity progress.

On the other hand volume lag is dependent on the progress of predecessor activity. Most lag is related to the progress of predecessor activity and therefore it is volume lag. Volume lag shall not be modeled by an activity because the progress is not on itself but on predecessor activity. Schedulers that do not know about volume lag use time lag as if volume lag, this is wrong and might lead to poor schedules.

Say pipe installation must start after 50 ft of excavation are done; it is not about time but about volume of work done by predecessor (excavation). That some passage of time elapsed do not necessary mean required work have been done. In such cases a good model will use volume lag not time lag.

GAO and many schedulers are still using old theories of the 1960's instead of using better and more modern models.

When GAO says “Moreover, if the critical path is missing dependencies or has date constraints, lags, or LOE activities or it is not a continuous path from the current status date to the finish milestone, then it is not valid.” they are in abysmal error.

There is nothing wrong with discontinuous critical path(s) if the lags, calendars and contractual milestones date constraints are correctly used.

GAO supports the archaic theories of “longest path” that breaks down under constraints other than predecessor/successor logic.

GAO suggestion to split activities as to eliminate the need for lag or to avoid long duration activities can make an activity discontiguous or intermittent when resource leveling. Activities competing for the same resource might delay the splits by leapfrogging the resources.The result is frequently a poor schedule.

That the critical path should be free of lags because they obfuscate the identification and management of critical activities is absurd. Links with or without time/volume lag can be part of the critical path. Without links you are essentially drawing a Gantt chart. Same as some activities can be on the critical path, some links can also be on the same critical path, critical links can be easily identified at the links table and most software allows you to thicken critical links similar to painting in red critical activities.

That there should be only one WBS for each program, and it should match the WBS used for the cost estimate and schedule so that actual costs can be fed back into the estimate with a correlation between the cost estimate and schedule is absurd.  

A WBS is nothing more than an organization or grouping scheme. There is no such thing as the ideal WBS. What a client might have in mind about WBS might be different to what a contractor might need.

Some commercially available scheduling software allows for multiple WBS structures, this solves any issue between client and contractor as there is always room for both.  

GAO is wrong in perpetuating the idea of a single WBS.

GAO says - The WBS is the basis of the program schedule and defines what is required as a deliverable.
WRONG - It is a well-defined scope of work (usually as per contract documents) and the means and methods necessary to deliver that defines what is required.

GAO says - In general, estimated detail activity durations for near-term effort should be no longer than the reporting period established by the program.

WRONG - Activity duration shall take whatever it needs to be in order to get better schedules. Duration of most activities is determined by the volume of work and resource production rates, there is no need to split activities to know progress, it is a lie, do not be lazy and measure volume of work done.

Artificial splitting of activities is wrong and might lead to undesired intermittent work under resource leveling. Trying to solve the issue using activity priorities will not always work.

Before leveling it looks like equivalent models.

https://postimg.org/image/v0cstphil/ 

After leveling they are not always equivalent.

https://postimg.org/image/ltui6fca5/

If using a database you can keep old schedule versions, as you should, this do not erases the history just clear them where not needed, where keeping them is a nuisance. Just compare new version against older versions and show deleted activities, cannot be any easier. Do you mean P6 cannot compare activities existing on different updates if activities are deleted?  If so then transfer the data to a better designed database. Even Excel can make it. Not all CPM software is so poorly designed.