We kept the plans and the spare engines. What we didn’t keep is the knowledge base of *why* they were built that way - the rationale for the design decisions as it were - and the skills to build an exact copy. We also didn’t keep the jigs, fixtures and machinery needed to make more - as the article points out, even the test stands were repurposed beyond the ability to reuse.
Without those, what you have is a bunch of useless paper. And that’s more or less what we had.
Can’t believe with the actual engines and plans we could not reverse engineer production of more units with modern manufacturing techniques.