Something to consider about pattern pairing. At the end of the manufacturing process the tubes were coated with sulfuric acid. This does two things. One, it creates a "skin" on the tubes, essentially a protective coating that appears to prevent rusting. If the tubes were then oiled before shipping I doubt any corrosion would occur during shipping. Two, the pattern is very visible, aiding in matching tube patterns. Due to these two points I suspect American makers would be able to make decisions about tube pairings, as the patterns would be visible to them when they made their selections from their stock of rough tubes, even though the tubes were paired in Belgium when they were shipped.
There must have been some percentage of tubes damaged due to shipping, resulting in some guns ending up with mismatched tubes.
