This could be an explanation, though I am not perfectly sure if I understood that issue correctly:

Adduct Ions [M+Na], [M+K], [2M+Na] etc. often show different concentration-dependent relative intensities within a mass spectrum and thus lead to rather complex calibration curves when only monitoring [M+H] in SIM mode. Including the intensities of further adduct ions to the "SIM" (term is actually not fitting any more) can thus improve the calibration curve's linearity.

Hi, Mayra, Scan mode can gives you the total ion current, which is a plot of the total ion current in each MS scan plotted as an intensity point.

SIM is set to scan over a very small mass range, typically one mass unit.  The narrower the mass range the more specific the SIM assay.  The SIM plot is a plot of the ion current resulting from this very small mass range.  Only compounds with the selected mass are detected and plotted. But SIM mode is typically more sensitive than SCAN mode for target ion(s).In your SIM case, if you only monitor [M+adduct]+, you only can see the a plot of the ion current resulting from this very small mass range, typically one mass unit.

The Adduct ion  typically presences when the surround conditions are suitable, such as pH, concentration of adducts. If the conditions to form the adduct are not existing, then you can expect the [M+adduct]+ disappear. 

Therefore, monitor or not adduct ions depends on your LCMS set up.

Hope it help you, Mayra

Adduct ions can be removed by changing some parameters like cone voltage, capillary voltage, DP, EP, mobile phases etc. To run SIM or SCAN mode depends on your requirement.