"No podría haber sido" AND "No pudo haber sido"
The above two phrases are used in a Mercedes add on TV.
In both cases they are translated from the same English phrase.
"It couldn´t have been".
Is there any reason why they are not the same in Spanish'
12 Answers
Ian, really there are two different structures in English too. If you consider that could can be either: past or conditional, the structure itself looks the same, but the meaning and tense is just as different as in Spanish.
It's a little tough to tell why without the context of the ad. "No podría haber sido" is conditional. If not for something, it couldn't have been. "No pudo haber sido" is a statement of fact. It couldn't have been, period. No ifs ands or buts.
In English we rely on context to convey the coditionality, in Spanish it's more explicit.
My limited Spanish does not allow me to express
1. "It can't have been." - which might express real surprise.
as opposed to
2. "It couldn't have been." - which might mean "It is impossible"
That is what got me going on this.
I need to give the context.
Two people are driving along in a modern Mercedes - they drive past a house and the passenger in the car sees a man that she thinks is James Dean and says "Was that James Dean'" the driver says "It couldn't have been" - "No podría haber sido." A woman who looks like Marilyn Monroe walks up to "James Dean" sees the Mercedes go past and says "Wasn't that a Mercedes'" to which James Dean replies "It couldn't have been" - " No pudo haber sido."
Does that help explain why there are two different structures for the Spanish and only one in English?
Did you hear this commercial in Spanish in Bolivia, Ian? Or was it subtitled?
Maybe there's some nuance of grammar that I'm not familiar with here, but I think they both have to be preterite. I don't think it makes any difference that it really could not have been James Dean (since he is dead), whereas "Dean" is conjecturing incredulously that it wasn't (couldn't have been) a Mercedes.
Where is Lazarus when we need him'!
To clarify
The ad was seen in Bolivia but could have originated anywhere. It was in English with Spanish subtitles.That explains a lot. I'm sure you have noticed/will notice many things that are incorrect in subtitles. I have often wondered who (or what machine) they get to do them. Quality will vary greatly.
I still wish Lazarus would opine on this and remove all doubt.
To clarify
The ad was seen in Bolivia but could have originated anywhere. It was in English with Spanish subtitles.
Rocco, I think you did not read my comment. Ian translated the spot himself, the spot is completely different in Spanish, and the people in the Spanish video are from Spain.
Por cierto, en español el anuncio simplemente usa un "seguro que sí" irónico.
En caso de traducirlo, Ian, yo hubiera dicho:
¿Esta no es Marilyn? Imposible! (no ha podido ser Marilyn)
¿Este no era un Mercedes? Imposible, no puede haber sido un mercedes.
Which is where we discover that it has been Ian who has translated the English ad 
Rocco is right, the conditional perfect, no podría haber sido would not be used as an isolated sentence.
I need to give the context.
Two people are driving along in a modern Mercedes - they drive past a house and the passenger in the car sees a man that she thinks is James Dean and says "Was that James Dean'" the driver says "It couldn't have been" - "No podría haber sido." A woman who looks like Marilyn Monroe walks up to "James Dean" sees the Mercedes go past and says "Wasn't that a Mercedes'" to which James Dean replies "It couldn't have been" - " No pudo haber sido."
Does that help explain why there are two different structures for the Spanish and only one in English'
i agree with kurt.
the way that i understand this is
como no podría haber sido, no pudo haber sido
maybe it's easier to understand it like this, if you think of it as one clause and not 2 clauses.
i'm not a native but this is the way i would translate this in my own language
but if i would tranlate it for an add i probably would loose the "como" also, to emphasize
i hope this helps
I think Kurt is on to something, Ian.
I would expect the first statement to be prefaced by something, possibly in the imperfect subjunctive, like, "Si no fuera por ..., no podría haber sido". Although this form (podría haber sido) is conditional, its function is like the conditional perfect. I can't quote you any rules on this, but I don't think this statement in the conditional can stand alone. I think the condition has to be stated, possibly in a subordinate clause.
On another note, do these statements end with "sido", or do they continue'
The above two phrases are used in a Mercedes add on TV.
In both cases they are translated from the same English phrase.
"It couldn´t have been".
Is there any reason why they are not the same in Spanish?
Could it possibly be both a conditional statement? No podría haber sido. Referring to wondering or conjecture? as well as a simple past tense sentence stating that "It couldn't have been" with No pudo haber sido. Maybe with marketing the car it leaves the consumer to wonder about what could have been as well as what it literally is'? Ok, could be stretching but somebody had to start with something. 
