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davidcyclebackLeon, silvering (which appears on cards that are actual photos, not machine printed cards) appears in different ways, intensities and patters, so it doesn't have to be the same on all items.
One last thing. As I recall these cards were shown with other trimmed Pre-War cards. If all of the cards came from the same scrapbook, or even scrapbook page, that would indicate the age of your cards.