So i've been wondering about last minute paid upgrade to world business class. On the KLM website it's written that if there are available places that people can get a paid upgrade and sometimes at a discounted price.

1. Has anyone has experience with this? Any idea what the discount is?
2. Is there a condition about the class you have booked your economy ticket in order to get a discount or is there no difference between V and Y ticket for instance?
3. Will the miles you receive afterwards be the miles you have booked before under the S or Y rate or does the person get the business class miles (meaning with 125-175% extra miles)?

Thanks in advance