That article says that the oldest ice in the core was 2.7 million years old. It actually mentions gaps in the record and ability to date ice only with a 100k ye

That article says that the oldest ice in the core was 2.7 million years old. It actually mentions gaps in the record and ability to date ice only with a 100k year margin of error. This does not imply that we have a continuous record of carbon levels for the past 2.7M years.