Please note that you wrote to the ResearchGate community, not to the RG team. However, I will attempt to answer your questions. At this moment, 5 articles and 2 preprints are attached to your profile (https://www.researchgate.net/profile/Carla-Rus/publications). ResearchGate's automated algorithms take over publications from some of the publishers' platforms, but this harvesting is far from being complete. Users are expected to add missing publications themselves. See this help page ("How to add research") for instructions how to add more published articles or unpublished research to ResearchGate: https://help.researchgate.net/hc/en-us/articles/14293005132305. The indication of a DOI is not mandatory.