I have decided that obsessing over pre-spend is just chasing a tangible solution to a question that doesn't have a concrete answer. If all QBs were the exact same bag, it would be logical to calculate a pre-spend number because there would be an obvious formula. But:
- There are multiple QBs (B and K at a minimum, and sometimes C)
- These bags come in multiple sizes and multiple styles (Sellier/Retourne, not to even mention the more out-of-the-box options)
- And multiple colors
- And multiple leathers
- With multiple hardware options
So all we're doing is spinning our wheels. Yes, pre-spend is obviously a factor, especially for first and second (and maybe third) QBs, but SA relationship is clearly more significant in the long run.
For the record, I'm still calculating my pre-spend because if you give me a tangible metric to track, I will track it.