The previously-posted links are dubious at best.
https://context.reverso.net/translation/spanish-english/aten... says nothing about “justifiable” being a translation for “atendible.”
https://www.definiciones-de.com/Sinonimos/de/atendible.phpThis link does provide “justificable” as a synonym for “atendible.” However, the RAE does not
https://dle.rae.es/atendible?m=form , and my copy of the
Gran diccionario de la lengua española, does not either. In my previous discussion entry, Cabanellas streches the senses to “aceptable” and “fundado,” but neither of these amount to “justifiable.”
So, either “justificable” is a modern or regional synonym for “atendible,” and the institutional lexicographic works have been too slow to incorporate this additional sense, or “justificable” does not amount to “atendible.”