Background: GLOBOCAN 2020 and Global Burden of Disease (GBD) 2019 are the two most established global online cancer databases. It is important to examine the differences between the two platforms, to attempt to explain these differences, and to appraise the quality of the data. There are stark differences for lip and oral cancers (LOC) and we attempt to explain these by detailed analysis of ten countries at the extremes of differences. Methods: Age-standardised incidence rates (ASIR) of LOC were obtained from GLOBOCAN 2020 and GBD 2019. Five countries with the greatest and smallest fold differences were selected. A systematic search of PubMed and Embase electronic databases was then performed to identify publications reporting the incidence of LOC in the selected countries between 2015 and 2022. Specifically, data sources of the articles were examined and evaluated. Findings: For LOC, greatest differences were found in Papua New Guinea, Vietnam, China, Pakistan, and Indonesia (group A). In contrast, the United States of America (USA), Brazil, France, Germany, and India (group B) had the least differences between the two databases. Interpretation: It is not surprising that when GLOBOCAN and GBD could not obtain high-quality or accessible LOC data from national or local cancer registries, as in group A, discrepancies would be seen between the two online databases. In contrast, where only minor differences were seen between GLOBOCAN and GBD, as in group B, presumptively due to those countries having well-established cancer registries and healthcare administrative systems, the literature is more consistent. Moreover, many studies have grouped lip and oral cavity with pharynx and categorised outputs as “oral and oropharyngeal cancer” or “oral cavity and pharynx cancer”. Those categorisations lacked subsite accuracy and failed to realise that oral cancer and oropharyngeal cancer have completely different etiological factors, pathogeneses, prognosis, and treatment outcomes. Funding: This research received no specific grant or funding from any funding agency in the public, commercial, or not-for-profit sectors, and the authors received no financial support for the research, authorship, and/or publication of this article.