The monitoring model and data products for the total electron content (TEC) in the ionosphere provide essential support for applications such as ionospheric delay mitigation in Satellite positioning and space weather monitoring. Some occasional situations may lead to the interruption of real-time ionospheric products. In order to ensure the continuity of real-time correction information, e.g., Real-Time Global Ionospheric Map (RT-GIM) provided by the International GNSS Service (IGS), the differential Slant TEC (dSTEC) from external GNSS stations is used to determinate the weight of RT GIMs in combination processing. Aside from the self-consistency validation methods, the external consistency analysis is required because a direct and truly external assessment is needed for weighted combination. Ionospheric VTEC observables from altimetry satellites and dSTEC from Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) are proved as reliable external references in ionospheric model validation, which shows quantitative consistency with GNSS dSTEC information in collocated analysis scenarios. The new cooperative GIM (RT-CASC) based on DORIS-dSTEC-based weight is presented in this work. The rapid GIM released by IGS (IGRG), JASON-3 altimeter Vertical VTEC (VTEC) observables and the STEC retrieved from 20 rover GNSS stations during the 001–270 Day of Year (DOY), 2022, are set as references to check the performance of different RT GIMs and the new combined one. The validations against three references show that the cooperative products have a comparable accuracy with a standard deviation (STD) range from 2.0 to 4.5 TECU, whereas the single GIM, e.g., IGRG, with an STD of 3.0–7.0 TECU compared to GNSS-STEC. Overall, DORIS dSTEC provides an independent reference for the combination of RT GIMs. In the future, it is also envisaged that DORIS data can be directly incorporated into ionosphere modelling.