Legal questions (none of which are answered by a default judgement):

a) Is the shape of a guitar even a valid copyright claim?

b) If so, Stratocasters were first 'published' when you had to follow forms to get copyright in the US. Where those forms followed? I don't see a copyright notice on this very early example [1] which is claimed to be original.

c) Copyrights generally don't have an enforce it or lose it requirement, but is there an impact on enforcability from the very long time that similar guitars have been available in the marketplace with no apparent enforcement?

d) added in edit. There's probably an international copyright question, too. Was the guitar 'published simultaneously' in a Berne member state as well as the US (which was not a member in 1954)? If so, Berne minimums apply, if the work is copyrightable, in member states (other than the US), otherwise, probably country by country?

[1] https://wellstrungguitars.com/guitar/stratocaster-sunburst-2...