Rarity has nothing to do with the material of the letters IMO. It has much to do with when the unit was formed, how many sailors were in that unit and how long the unit was in existence. Therefore, a tally requires much research into exactly what the unit was--it is obvious with a major ship, not so obvious with the smaller and more short lived units.
Then you must also factor in the material timeline provided by Markus.
My two cents.
John
Then you must also factor in the material timeline provided by Markus.
My two cents.
John
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