Adding conditional column with either value from other column OR the value from the row above

Yes I am. We have 4 types of mutations that influence the stock level:

1. Purchase: receiving purchase orders
2. Production: our own production from our shop factory
3. Sales: sales via our Service Deparment
4. Project: Usage on projects that are being assembled

My idea is

• That mutations are done in planned order, so I can put them ordered by date and see how stock fluctuates
• For mutations of type 3 and 4 there is a problem if after the mutation stock is below zero (of before the mutation, the mutation amount is bigger than the stock level)
• I want our Purchase Department to react and my first impression is that I can have up to 2 possibilities:
  • If there is a purchase reception planned before the expected stock shortage: I can try to ask the supplier to increase the amount on that Purchase Order, but I need to now which Purchase Order I need to look at
  • If there is a purchase reception planned after the expected stock shortage: I can try to ask the supplier to deliver earlier, but also for this goes that I need to know which Purchase Order to look at.
  • Also for the Purchase reception that is planned after the expected stock shortage: if the difference in dates is less than or equal to 7 days, I can neglect them because for me that is still acceptable and not worth the effort to get the delivery a few days faster.

I hope you have an idea now of what I try to achieve

Hi lbendlin, can you tell me whether it is technically possible? Or do I need more, additional data? I'm still hoping you can help me out.