The 6538 was a professional's watch: 200 meters, the oversized 8 mm crown, no crown guards. Then Dr. No happened. Sean Connery wore a 6538 on a nylon strap famously borrowed on set, the watch returned in From Russia With Love, Goldfinger and Thunderball, and the reference has been the Bond Submariner ever since. Sixty years of that association sits on top of a production run of only about three years.
Short run, hard professional use, and the most famous nickname in watch collecting is the recipe for a reference where honest examples are outnumbered by optimistic ones. Dial swaps, redone lume and married cases chase this watch the way added mintmarks chase a key-date coin.
The most famous dive watch ever made, which is exactly why skepticism is the correct opening position. Buy the documentation, the seller's reputation and the expert opinion; the romance comes free afterward. And know that the big crown itself is a spec, not a guarantee - it appears on the 6200 and 5510 too.
Production windows and specifications compiled from documented collector references and period catalogs, cross-checked across independent sources; manufacturer records for this era are approximate by Seiko's own account.