It’s not common. Most will have rear speakers but some (inc. my own) left the factory with front speakers only. The SE did not come with the 8-speaker system as standard, though most got them.
The stereo head unit can be a useful clue.
Any A2 SE with the double-DIN Symphony unit will have rear speakers. Any A2 SE with a factory-fitted single-DIN Concert II CD player will also have rear speakers. The only A2 SEs that didn’t get rear speakers by default were those made with the Chorus tape deck.
However, even with the Chorus tape deck fitted, it was still possible to specify rear speakers as an optional extra, so not all A2s with the Chorus tape deck only have speakers in the front doors.
Of course, all these years later, things could have been swapped about. An A2 that left the factory with a Chorus tape deck and front speakers only could easily have had its head unit changed for a Concert CD player, so seeing a Concert in photos isn’t a hard guarantee that the car will have speakers in the back doors.
That’s all a little vague, but hopefully helps somewhat.
Best wishes,
Tom