Irenaeus mentions churches in Spain and Gaul. Romans 15 records Paul's plans for Spain. These establish different things: an intention and a later report of communities. Neither is a complete genealogy. H05 Romans 15:24,28
The proposed Nazarene-to-converso connection asks us to investigate who moved, when, which practices traveled and whether records link communities across generations. A geographical possibility is a beginning. A named person or document connecting two communities makes the case stronger.