So far, the operational combination of the monthly GRACE, or GRACE-FO gravity field solutions by the Combination Service of Time-variable Gravity fields (COST-G) has been performed on the solution level. The originally foreseen combination on the normal equation (NEQ) level suffered from the very diverse and not realistic formal uncertainties, which hampered the application of Variance Component Estimation (VCE) and made the use of empirical weighting factors mandatory. Meanwhile, empirical noise models that enable the determination of realistic formal uncertainties are available from several GRACE-FO analysis centers. Experimental NEQ-combinations confirmed the applicability of VCE for the GRACE-FO combination and also the combination with SLR turned out to be feasible without the use of empirical weighting factors. The combination of the future GRACE-C and NGGM missions on the NEQ-level is a prerequisite to generate gravity field solutions of the MAGIC constellation. Consequently, the combination of NEQs from different Analysis Centers (ACs), including also SLR, will be the goal of future COST-G releases, but relies on the cooperation of the ACs to provide their NEQs and to apply realistic noise models.