I am not sure I understand your comment. Surely, from the tildes and the ortographic rules one can figure out which syllable has the stress (non-ambiguously).

I am not sure I understand your comment. Surely, from the tildes and the ortographic rules one can figure out which syllable has the stress (non-ambiguously). In your example, recibí specifies where the stress is (last), even if it is the first time one sees this word. Same for recibo (second-to-last) or repopo (invented word). The tilde rules (vowel, ending in n or s, plus diptongos, hiatos and specified exceptions) are consistent. There is no breaking of rules in verb conjugations. Most are stressed second-to-last, but that is not the rule, just an observation. Or am I misunderstanding something?