747-100s had only one small emergency exit up there. This limited capacity of bubble to a max of 16. -200s/SPs had two large exits which increased capacity. -300s/400s stretched the bubble and capacity increased again.
RAT 5, I think that when the 200s were introduced business class, as we know it, was still quite a few years away.
Can you remind me of which airlines used the bubble for crew-rest? IIRC the original operaters all began with a lounge up there, including the piano!