Is the refence to the future the only thing that distinguishes between whether it describes a comleted actions in rhe past or future? thank you

Hola Emanuel,

Yes, that reference to the future is what makes it refer to a completed future action. If we had no future reference we would think it is referring to the past. For example:

Espero que hayan empezado a construir la nueva urbanización antes de septiembre.

(referring to the future)

Espero que hayan empezado a construir la nueva urbanización.

(referring to the past- unless it is omitting the future reference because it is assumed, i.e. it was mentioned before in the conversation so there is no need to repeat.)

Saludos,

Inma