The end of the last sentence in the issue description should read "...as in the tables with Type definitions.".

All types are defined following the common conventions in the OPC UA specifications.

The table with the structure fields never indicates a base DataType (e.g. Table 32 ReaderGroupDataType Structure). This table only defines the fields.

The DataType Node and the type relation is defined in an additional table (e.g. Table 33 – ReaderGroupDataType Definition).
This table clearly indicates that the ReaderGroupDataType is a subtype of PubSubGroupDataType.

I disagree, for following reasons:
1) no matter what the conventions are or were, the missing base datatype is very confusing when somebody new uses the spec,
2) The argument about common conventions is weak, because structured datatypes I could find in other parts of the spec only derive from BaseDataType, so the commonality does not exist in practice,
3) I could not find a rule that would define such a convention (but it might exist)
4) There is no logical reason why tables for object types/variables should indicate the base type, and those for datatype not. In fact, it's less important for object types, because it is clear that the address space may contain other references/nodes not listed in the table But if you put a sentence saying "this is the XXXX structure" and a table header "XXXXDataType" over the table, you really expect that what you see is what is in the structure - and not just part of it.
5) The DataType node table (the one that has the base datatype) is not what the user reads when he is trying to understand the concepts. It has a different purpose - for the actual coding (and creating a nodeset). Understanding the concepts is difficult without being aware of the base datatype.

There is not a single table in none of the OPC UA parts that define the base type as part of the table that defines the structure fields.

TBD
Add this to the description e.g. Subtype of PubSubGroupDataType defined in 6.2.4.7.
See 6.2.7.2.1 ReaderGroupDataType

Added reference to base type to all description fields of the structure name for all derived structure types.

Agreed to changes in meeting.

This was not fixed for at least DataSetMetaDataType.

Added missing reference to base type of DataSetMetaData:

Subtype of DataTypeSchemaHeader defined in OPC 10000-5.

Agreed to changes in Dallas meeting.