Tagging what is in a Revit Key Schedule

What, no Shared Parameters in Key Schedules?  It is a total pain.  If you'd like Autodesk to fix this Revit Roadblock, please vote for the enhancement on their Revit Ideas:
Please Fix Key Schedules
 This request has been 'Under Review' for several years, and it needs kicking along.

I have been endlessly frustrated by the fact that you cannot include shared parameters in Key Schedules in Revit.  This means that anything you put into a key schedule can only be used in other schedules - it cannot ever be tagged.
Or so I thought. . . . .

I recently discovered that you can add some system parameters to key schedules, which means that you can use those in schedules and tag them too.  As with most things Revit, the rules for this are weird and (not so) wonderful.

Rule no. 1:   

Shared parameters, have a secret GUID that ensures their uniqueness - you have to add them to schedules by picking them from a list of already available parameters or by adding them from the shared parameter list.  Likewise system parameters in a schedule or key schedule need to be picked from a list of available ones.  It is only too easy to create new parameters by typing in names that seem to have the same name as system parameters - you won't know which is which, as they appear together in lists.  It is only when you start populating them or using them in (key) schedules when you realise your mistake.
For this reason it is really important never to create your own parameters that are the same name as system (or shared) parameters.  With shared parameters it is a little easier as you can go into the definition and check if it was shared or not.

Rule no. 2:  

Once you use a system parameter in one key schedule, it cannot be used in other key schedules of the same category

When you first create a key schedule, you get a list of available fields on the left.  This is a jumble of system parameters and project parameters that you might have created (but not shared parameters).  Because the list is radically different for each category (and varies with subsequent key schedules), I never realised the significance of that list

Rule no. 3:  

Different categories allow different system parameters to be used in key schedules.  There is no rhyme or reason as to which ones will work - you just have to know.  For most categories it is just "Comments".

Categories that do not allow any system parameters in a key schedule include:

• Grids 
• Levels

Categories that allow 'Comments' as a system parameter in a key schedule include (NB. I only checked the ones that show up when listing "Architecture" categories):

• Assemblies
• Casework
• Ceilings
• Columns
• Curtain Panels
• Curtain Systems
• Curtain Wall Mullions
• Detail Items
• Electrical Fixtures
• Entourage
• Floors
•      Floor Slab Edges
• Furniture
• Furniture Systems
• Generic Models
• Lighting Fixtures
• Mass
•      Mass subcategories (I only checked Mass Floors)
• Mechanical Equipment
• Parking
• Parts
• Planting
• Railings
•      Handrails
•      Supports
•      Top Rails
• Ramps
• Roofs
•      Fascias
•      Gutters
•      Roof Soffits
• Site
•      Pads
•      Property line segments
•      Property Lines
• Specialty Equipment
• Stairs
•      Landings
•      Runs
•      Supports
• Structural Beam Systems
• StructuralColumns
• Structural  Connections
• Structural Foundations
• Structural Framing
• Structural Rebar
• Structural Stiffeners
• Topography
• Walls
•     Wall Sweeps
• Windows

Categories that allow multiple system parameter in a key schedule include:

• Areas

         Wow, the programmers really spoiled us by allowing the use of the Name System Parameter - but don't get too excited because this has to be shared across all Area Schemes.  So if you use it for a Rentable Area Key Schedule, it will not be available for a Gross Building Area key schedule

• Doors

         Out of all the 40+ door system parameters, they gave us those!  How useful.

• Electrical Equipment

          It looks like the Electrical engineers are being favoured for a change.  But not the mechanical engineers who only get 'Comments' for their equipment.

• Plumbing Fixtures

• Rooms

Now this should give us something to work with - although we only get text and material parameters, that should be very useful as those are the ones we most likely want to tag.  I can't imagine wanting to put the finishes into a key schedule as most likely each room could have different finishes - but if you have say a hospital where there are many similar rooms, you might create a key schedule of room types, and those could have preset finishes in a key schedule?

The list of categories/system parameters above is not comprehensive - structural and MEP engineers will need to do some inestigation on the categories that do not show up when the list is restricted to "Architecture" categories.

Conclusion

Well, at least we do have some system parameters we can use in Key Schedules.  However the list is very limited, so use them wisely - plan your schedules and tagging needs before you start creating key schedules.  Don't forget that if you have multiple key schedules for a category, the available system parameters can only be used once per category (not once per key schedule).

An example of when you might use one of these precious system parameters could be for rooms or areas - naming the apartment type as say '1 BED' or '2 BED'.  This value could then appear in a schedule, a tag and in properties.  Associated with each apartment type could be all sorts of standards such as minimum areas, rates and parking requirements etc - these would only appear in schedules and properties (and they could be there just for use in calculations).  Things you would not include in the key schedule would be unique information that varies per room or area.