There's absolutely no timeline implied in this panels lmao. Sengoku was talking about the Rocks incident after which the Navy tried promoting Garp and we know for a fact that they did it during the Shiki fight as well but there's absolutely no confirmation that when Akainu, Aokiji and Kizaru reached their prime the Navy has tried even once to promote Garp.
He was simply surpassed as he got gradually weaker and that's that.