Question on Catholicism (Yay!)

[Kaine for Senate '18]

I thought it was that Stephen died before he could become a Bishop (or something like that).

[Kaine for Senate '18]

The list of popes fascinates me. (Does it to anyone else?) But there's one thing that confuses me. What difference between Pope-elect Stephen and Adrian V is there that makes the latter Pope but the former a simple priest?

Stephen had not yet been consecrated a bishop at the time of his death.  It took a long time for the Vatican to hammer the system out, as evidenced by the irregularities in the numberings of Stephens and Johns (there is no John XX), but it was decided that, if you were a bishop when proclaimed Pope, then you automatically became the pope, you just had to be formally installed at the Lateran.  If you were not yet a bishop at the time of your being proclaimed pope, then you were not the Pope until becoming a Bishop.

The latter circumstance will likely never happen again, as a non-bishop hasn't been named a Cardinal is several centuries and a non-Cardinal hasn't been chosen in at least as long.

Cool!  I was right