My GPS tracks show 23.7 km from Arcade to Combarro and 9.54 km from Combarro to Armenteira. However, exact GPS distances should always be taken with a slight grain of salt. They depend on where exactly the start and finish points are selected, slight deviations in the walking path, and they have to take into consideration standard GPS error.
When I develop GPS tracks for use in my projects I start with my own track and then collect tracks provided to me by others and do a programmatic sort of 'averaging' on them to reduce GPS error. But the larger the distance involved, the larger the error margin will be regardless. Hence why you can see differences of half a km or more when looking at the 'same' stage from different sources.
Also, distance doesn't always equate with difficulty. Elevation gain / loss is important to consider as well as the quality of the path itself (rocky, paved, muddy, etc.).
Enjoy the Espiritual – it's a very nice detour and well-worth the extra walking.