The first-time or amended determination of Inheritance or Gift Tax for the previous acquisition is no event with retroactive effect which allows the determination of Inheritance or Gift Tax for the subsequent acquisition.
According to the Federal Finance Court, a tax assessment notice regarding the previous acquisition within the meaning of § 14 Inheritance and Gift Tax Act (IGTA) is no basis (§ 175 para. 1 no. 1 General Fiscal Code) for the determination of the subsequent acquisition.
Excursus
Multiple acquisitions by the same person within 10 years are added together pursuant to § 14 IGTA. Hereby, advantages of tax allowances and progression through multiple partial acquisitions are avoided. Only if an event with retroactive effect occurs, e.g. according to § 13a IGTA (violation of minimum total payroll), the tax assessment notice of the subsequent acquisition can be amended, even if the limitation period has already expired. As in the underlying case the tax assessment notice was just modified, no amendment is permitted for the subsequent acquisition.
For more details see Koeniger, The German Inheritance and Gift Tax, 2017, p. 237 et seqq.