We have employees with competencies:

Pete      Welder
          Carpenter
Melissa   Carpenter      

Assume they both work 40 hours/week, and have not yet been assigned work.
We need to report the availability of these competencies, expressed in hours.
As far as I can see now, we can report this in two ways:

Method A. When someone has multiple competencies, count them both.

Welder    40 hours
Carpenter 80 hours

Method B. When someone has multiple competencies, count an equal division of hours for each

Welder    20 hours
Carpenter 60 hours

Method A has our preference:
- A good planner will know to plan the least available competency first. If 30 hours of welding is planned, we will be left with 10 welder, 50 carpenter.
- Method B has the disadvantage that the planner thinks he cannot plan the job when 30 hours of welding is required.

However, if we report this we would like to give an estimate of the reliability of the numbers for each competency, i.e. how much are these over-reported?

In my example A, would I say that carpenter is 100% over-reported, or 50%, or maybe another number?
How would I calculate this for large numbers of competencies?
I'm sure we are not the first ones dealing with this, is there a 'usual' way of doing this in planning?

Additionally:
- Would there be an even better method than A or B?
- Optionally, we also have an preference order of competencies (like: use him/her in this order), Pete could be 1. welder 2. carpenter. Does this introduce new options?