You might just not remember why you came up with such a solution. When creating, we are recycling impressions all the time without realizing it.
Your logo is copied
Ferdinand Vogler

Beyond stealing and copying, there’s a third possibility, which you don’t seem to acknowledge: Two designers working at different times may independently arrive at similar solutions. Just because Logo 2017 resembles obscure Logo 1975 does not necessarily mean that Designer 2017 ever even encountered Logo 1975, much less being subconsciously influenced by it. As you note, visual language rely on the common semantics of visual forms. So by their nature, visual forms will tend to reoccur, even in isolation from eachother’s direct influence.

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