Hi Herman...I do think the wedding scenario is unlikely, more likely to be Officer to Officer, and as they would be very close friends then also likely to be the same rank.
I have never seen a rank specified on an 'S/L'dedication, only on an award-sword for some kind of achievement.
Young Officers, say, of Leutnant rank could well come from wealthy families and be able to afford such gifts. Here is an example of an IOD89 with an 'S/L' dedication on one side and motto (To the Enemy Defiance To the Friend Protection)on the other and some nice gold wash half-way down the blade. Also of interest is the recipient's initials on the grip cap to be used as an ink stamp.

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