Not explicitly related to my specific case but also stated on the KfW website:
Can I conclude delivery and service contracts or the purchase contract before submitting the application?
Yes, initial delivery and service contracts or the purchase contract (for the first purchase) can also be concluded before submitting the application under the conditions listed below.
Exception rule for delivery and service contracts
For delivery and service contracts, you have two options:
1. documented consultation
Have you documented your financing consultation with a KfW form? Then you can subsequently conclude initial delivery and service contracts. However, construction may only begin after the application has been submitted.
2. suspensive or resolutive condition
Have you agreed on a suspensive or resolutive condition? Then you can conclude delivery and service contracts before submitting the application. However, construction may only begin after the application has been submitted.
Please note: The amendment of delivery and service contracts by subsequently adding a suspensive or resolutive condition is not permitted.
For the formulation of suspensive or resolutive conditions, we provide you with a non-binding sample formulation: