I suspect 11B didn't have them installed yet. It looks like an after thought at the factory and likely from road use feedback, IMO. Below is what I wrote in a recent thread on those shields:
Looking at my 04B LOS survivor and 5B NOR restored, neither have it installed nor does the 04B survivor look to ever have had it. Looking closer to the AIM revision record it states those items related to the splash shield were "added" 3/30/67. That would explain it not showing up on my 04B yet and I suspect it wasn't installed on the 05B as well due to not being in the implementation start (my notes do not even mention it existed when I disassembled the car in the early 80's).