To clarify just a tad... The Pilgrim Office, a part of the Cathedral bureaucracy only issues Compostelas to pilgrims who can document that they walked at least the FINAL 100 km or 200 km if on a bicycle, INTO SANTIAGO.
Consider that, since about the year 850 AD (mas o menas), the object of the
Camino de Santiago is to arrive at Santiago, originally to venerate (NOT worship) the remains of the Apostle of Jesus Christ, St. James the Greater, entombed beneath the great altar in the Cathedral. So, Santiago de Compostela is the final destination, as regards obtaining a Compostela, not a point along the way.
Given the circumstances offered in the OP, the journey needs to be in the other direction, and at least 100 Km on a pilgrim route, to qualify for a Compostela. In addition , during those final 100 km, the pilgrim must obtain TWO SELLOS (stamps) daily in their pilgrim credential. Farther out, beyond the 100 km limit set by the Church, one sello daily is adequate.
I hope this helps.