Can we avoid DIF by using a panel design, without vignettes?

A two (or more) wave panel study enables one to estimate the effects of explanatory variables that vary over time, without using anchoring vignettes. The problem is that a differencing design is required, meaning that the absolute level of the variable being measured (health, efficacy, etc.) cannot be estimated. Nor can the effects of explanatory variables that are fixed over time (such as sex, education level at first interview, etc.) or change predictably over time (such as age).