Washington Treaty timing mattered for 18-inch battleships

How would the Washington Naval Treaty change if newer 18-inch battleships had already been completed?

The treaty would have been much harder to settle because completed 18-inch ships would make smaller limits less attractive and make older battle lines look weak.

The treaty had to arrive before the Royal Navy's planned 18-inch-gun ships entered service. Once such ships existed, Britain would have had little reason to discard them, and other navies would have wanted comparable weapons. The settlement depended on a narrow political and technical opportunity rather than an inevitable postwar agreement.