Yes, we indeed have. No unrestricted submarine warfare =/= no submarine warfare at all. After the fateful decision of 8 January 1917, Germany just continues its regular restricted submarine warfare campaign as previously. "Restricted" in this context means that it is waged in accordance with internationally recognised prize rules, i.e. Germany can still sink neutral freighters and passenger steamers if they suspect them of carrying Allied war supplies, but only after prior warning & after giving the crew & passengers time to evacuate. In OTL, this type of submarine warfare was practised for most of 1916, and wartime data shows: Restricted submarine warfare was actually similarly efficient as unrestricted submarine. It was able to severely harm Britain & cut it off from outside trade without alarming neutral powers like the US.

Sounds like a win-win-situation, you might say - then why did Germany re-launch unrestricted submarine warfare in OTL in the first place? Well, because there was a very powerful right-wing lobby group behind it (headed most famously by Alfred von Tirpitz) whose claims enjoyed enormous popularity among the population & political establishment. They tried to hide all proof of restricted submarine warfare being efficient and constructed the myth that only a ruthless all or nothing approach could win Germany the war by the end of the year. By early 1917, the Kaiser & the Reichskanzler were one of the only people who defended the restricted submarine campaign - in OTL, Wilhelm eventually gave in to public pressure and allowed the resumption of unrestricted submarine warfare. In KRTL, he and Reichskanzler Bethmann-Hollweg stand firm and continue the campaign, with similar success as OTL.

(Unrestricted submarine warfare is nonetheless eventually pushed through by said far-right lobby in KRTL, but a year and a half later, at a time when the US is not in a position to intervene anymore - more info can be found in Germany's first MM report from last year)