Excellent information - here is a direct quote from the website above.
"
The El Camino de San Antonio Missions is a program offered by the Archdiocese of San Antonio that encourages and supports pilgrimage to these sacred sites. Today, the four missions churches still exist as active parishes.If you are interested in thiis program please visit the Padre Margil Pilgrimage Center located directly behind Mission Concepción, or their website.
San Antonio is the only place outside Europe where one can officially begin walking the El
Camino de Santiago. Pilgrims who walk the entire route in San Antonio receive 30 km credit toward the Camino Ingles (English route) along the El
Camino de Santiago, making El Camino de San Antonio part of an official route of the Camino in Spain."
It clearly says here that the credit on the USA mission walk in San Antonio only applies for the Ingles.