As far as I can tell, you are the only person in this thread who actually skimmed the paper. Thank you for pointing this out!

The API clearly delineates the March and June versions. The paper authors ran tests on different API versions. The fact that these versions are different is clear & transparent. Anyone can use the March version of GPT by calling the API.

gpt-4-0314: very slow, smart

gpt-4-0613: fast, less smart