Based on your comment, I modified my scene to better test the issue and I think I’ve made some important observations. The following video has the particle Lifetime keyframed to 55 at frame 50 and 15 at frame 150, under a Constant interpolation type (please excuse the suddenly teleporting rocket at the end):
Note how in the viewport version you get a ‘ring’ of smoke at the transition, while in the rendered version the entire cloud shrinks immediately. This looks to me as though the simulated version of the effect adjusts only the Lifetime value of newly-created particles, while the baked/rendered version adjusts the values of all currently active particles as well.
Unless there’s an option somewhere to change this behaviour I think we’ve found a bug in Blender; the question is whether it’s a product of the baking function simulating the particles differently to the viewport simulation (in my opinion unlikely since the original version of the effect remains – and is made constant by the bake – until the file is closed and reloaded) or in the process by which Blender saves the cache data (I don’t personally know how Blender does this so I can’t say for certain, but I did find this bug report which suggests it’s had other issues with cache saving in the past, even if the exact situation isn’t quite the same).
