Whether § 28 SPFG permits conversion of old global-budget subsidies used for investments into a loan
Yes. The provision can cover altrechtlich granted global-budget subsidies, if they were used for investments within the meaning of the VKL and those investments still have a remaining value.
The wording does not exclude subsidies paid under a global budget. The purpose is to prevent double financing after the new KVG funding system, and equal treatment of hospitals supports a broad interpretation.