Here is the quote above with additional context :-

"NASA’s Orbiting Carbon Observatory, 2 (OCO-2) provides the most complete dataset tracking the concentration of atmospheric carbon dioxide (CO₂), the main driver of climate change. Since its launch (July 2014), OCO-2 measures sunlight reflected from Earth’s surface to infer the dry-air column-averaged CO2 mixing ratio and provides around 100,000 cloud-free observations.

However, the OCO-2 data as observed by the on-board instrument have large data gaps in coverage due to the narrow 10-km ground track and an inability to see through clouds and aerosols. To provide a gap-filled view of Earth’s carbon cycle and atmosphere NASA’s Global and Modeling Assimilation Office (GMAO) ingests OCO-2 retrievals every 6 hours with a modeling and assimilation technique and derives the Gridded Monthly OCO-2 Carbon Dioxide/OCO-2 GEOS Level 3 product."

According to your source, the satellite provides the most complete dataset.