No Dan, Theo is right here. A factor of 4 in the amplitude means 12dB:
20*log10(4) = 12 (or, alternatively, if you want to consider to equation for converting instantaneous powers into dBs it would be 10*log(4^2) = 12)
That being said, now talking about headroom and maximum signal amplitudes when stacking four notes is a bit different compared to what the OP was about, or what I thought the OP was about.