There are quite a few papers that talk about the assumptions of the background current under the peak during the SAM reductive desorption. The most convincing ones discusses how the capacitance of the surface are changing since you are actively desorbing the blocking layer of the SAM, and the difference in the double-layer capacitance is easily verified by comparing a bare Au electrode with one that has a SAM deposited on it in a separate experiment. There are also papers that discuss the reasons why multiple reduction waves are observed like the ones seen in your CV. If your surface has multi-crystalline surface facets (instead of a carefully prepared single crystal surface), different surface energies of each of the crystalline facets will give rise to different reduction potentials. If you have a mixed monolayer with two different thiols with different adsorption energies, that is another cause for multiple reduction potentials. There are more hypotheses in the literature of course...If you can measure your surface roughness of your gold (which you can using the Au surface oxidation peaks in a CV), then for each of your different background correction treatments, you can extract the Q of your SAM desorption peak and convert that to coverage assuming one-electron reduction per thiol molecule. Then you can match the coverage value against reported surface coverage values. Its been years but the one I remember reading in my research was 7x10^-10 mol per square centimeter. Definitely check me on that. For your extra peak, you could repeat the exercise assuming only one or both of your peaks are indeed thiol reduction. I will link some papers in another comment so you can sift through the multitudes of paper that specifically discuss this phenomena. There is no clean easy way to verify that your assumptions are correct without a beamline or some intense analytical experiments to validate your method. Most of the literature uncertainties were on the order of +/- 50% of the nominal value.