New designs with any kind of legacy are called green projects or greenfield applications. The part of the project that already exists is commonly called brown projects. It is, obviously, simpler to apply Domain-Driven Design (DDD) and patterns on green projects than to legacy projects.
The shared data pattern is a controversial pattern when we talk about microservices. It would certainly be considered an anti-pattern if we applied it to a green project. However, it is a pattern that should be considered as a temporary pattern for legacy applications that are in a transitional phase.
The great concept behind this pattern is to use the same physical structure for data storage. This pattern can be used when there is some doubt about the structure of the data, or when the communication layer between the microservices is not well-defined.
The following diagram...
