I just realized that using Google to find this answer is silly - Control surface limits are in the TCDS.
Per the TCDS, the 182R has 40 degrees up through S/N 18268055, and then has 38 degrees (Hmmm) and that would have been the changeover between 1981 and 1982. Oddly enough, the TCDS also says the 182S and 182T have 38º, not 30. Am I misremembering that this switched on both the 172 and 182?
@Katamarino I think yours was upgraded with the P-Ponk engine, right? I thought I saw somewhere that flaps became limited to 30 with that STC, though I can't find anything official. Maybe that's why you've got 30?