Two years can affect a plan in several directions at once: more contributions, fewer withdrawal years, additional earnings, and possibly a different Social Security claim strategy. A side-by-side comparison helps separate the financial tradeoff from the lifestyle decision.
Use one consistent set of assumptions for each scenario. That makes the difference easier to understand and gives you a clearer starting point for an important conversation.
Build a private plan, compare two dates side by side, and review the assumptions behind the result.