Is DC voltage gain the change in offset and AC voltage gain the change in amplitude of the input waveform?
Not exactly. The two gains are exactly the same thing, in truth; the ratio of output signal to input signal. If DC and AC gains are given separately, that implies that some filtering is present, in order to attenuate signals at unwanted frequencies, or just as a consequence of the parasitic elements that are due to the circuit geometry. AC gain can be read as being the output over the input when the operating frequency is high, and DC gain is output over input when operating frequency is low.