Does Auto-Green guarantee a green every shot?

No. yew's own description: "Auto-green is the mod that most of you are looking for — it automatically times and fully performs shots for you. It is not going to work in 100% of situations; good values should have you at ~70% with auto-green."

The rest depends on your jumpshot, the required in-game settings, and how well your value is tuned. Contested shots and shots taken while the stick is outside the centre are not what the standstill page is for.

Treat the ~70% figure as yew's expectation for a well-tuned setup, not a promise.

Source: yew's published settings.