"Debe haber estado dificil" vs "Debió estar dificil"

Question

"Debe haber estado dificil" vs "Debió estar dificil"

I'm confused between these two sentences. Are they the same? I'm trying to translate: It must have been difficult. As in: You worked 15 hours? It must have been difficult.

Answer 1

Both:

(1) "Debe haber estado difícil"

and

(2) "Debió estar difícil"

are correct Spanish versions of:

"It must have been difficult",

the only slight difference being that, with the modal verb in the present in (1), the speaker is making a present assumption about a past event. Instead, the past form of the modal verb in (2) places the assumption in the past. The result, however, is similar. My impression is that in (1) there is a stronger emphasis on the present deduction, while in (2) there is a stronger stress on the past certainty.

And there is also the equally correct:

(3) Debió haber estado difícil.

Something similar occurs with "poder", which expresses possibility:

(1) Puede haber sido una gripe. (It may be the case it was a flu.)

(2) Pudo ser una gripe. (It was probably a flu.)

(3) Pudo haber sido una gripe. (It may have been a flu.)