How to work around Pydantic's lack of high-level support for Unpack tuples?

Use handler.generateschema(...) (not Model.pydanticcoreschema) and build a variadic tuple schema with variadicitemindex=1. The “class not fully defined” happens because you’re grabbing the other models’ core schemas too early.

from future import annotations
from pydantic import RootModel
from pydanticcore import coreschema
class ParsedDatFile(RootModel, frozen=True):
    root: tuple  # (ClrNamePro, Game, Game, ...)
    @classmethod
    def getpydanticcoreschema(cls, sourcetype, handler):
        return coreschema.tupleschema(
            itemsschema=[
                handler.generateschema(ClrNamePro),  # first item
                handler.generateschema(Game),        # repeated item
            ],
            variadicitemindex=1,  # repeat schema at index 1
            minlength=1,           # must have at least the first item
        )
ParsedDatFile.modelrebuild()

That’s it: first element must validate as ClrNamePro, and it may be followed by zero or more Games.