The mystery is solved, I think.
If you look at my first post I mention the huge seams between the armour plates which some modellers thought they would be welds. These aren't armour plates, they're the outer skin of the anti-torpedo bulges and as such would be relatively thin compared with the armour plate (10-12 inches on this ship). The bulges would be part filled with water, the idea being that they would absorb and dissipate the forces generated by an exploding torpedo, isolating it from the main hull ( not a very good explanation, but the best I can do). These bulges were added sometime during the 1930's and were certainly there by 1937.
The detail we can see is either a joggle in one plate so that it can be riveted to the adjacent plate(s) or a joining strip (strake) so that two plate can be riveted together, one row of rivets in the first instance or two in the second.
Whichever method, they're quite prominent as the pics show.
Haddock.
On occasions, one side would be completely flooded, inducing a list, thus increasing the range of a broadside!!