Consider:
- Victorian England: 1837-1901
- American Old West: 1803-1912
- Meiji Restoration: 1868-1912
- French privateering in the Gulf of Mexico: ended circa 1830
Conclusion: an adventuring party consisting of a Victorian gentleman thief, an Old West gunslinger, a disgraced former samurai, and an elderly French pirate is actually 100% historically plausible.
It really just comes down to whether a given individual or group is looking for reasons to include, or reasons to exclude. Hypothetical groups like these can go a lot further than this, too.
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