I was unsure whether the stages are correct and the distances so I went on the Gronze website to check them.
They were slightly different as mentioned before but most definitely achievable.
Here is what I found about the 13 stages of the Camino de Primitivo:
Day 1: Oviedo – San Juan de Villapañada 27.0 Km
Day 2: San Juan de Villapañada – Salas 18.2 Km
Day 3: Salas – Tineo 19.8 Km
Day 4: Tineo – Pola de Allande 26.4 Km
Day 5: Pola de Allande – La Mesa 21.6 Km
Day 6: La Mesa – Grandas de Salime 15.2 Km
Day 7: Grandas de Salime – Fonsagrada 27.6 Km
Day 8: A Fonsagrada (Padrón) – O Cádavo Baleira 25.4 Km
Day 9: Cádavo Baleira – Lugo 31 Km
Day 10: Lugo – San Romao da Retorta 19.6 Km
Day 11: San Romao da Retorta – Melide 28.3 Km
Day 12: Melide – O Pedrouzo 33,3 Km
Day 13: O Pedrouzo – Santiago de Compostela 19.4 Km