I understand the IPR point. However I think this really depends on what form of protection they wish to rely upon. If they have patented some key aspect then that aspect will have had to appear in the patents - which are openly available unless there is an exception issue like National Security - which seems unlikely here.
Copyright might prevent anyone else from duplicating, say, the *PCB*. But I doubt it can prevent someone else examining the circuit and making their own circuit diagrams of it. What has been sold and labelled is the physical system, not a circuit diagram.
The reality, of course, is that large equipment makers routinely take apart 'competing' products to examine them. Just that they then use the info when making their own designs, without publishing (or patenting) what they found.
Plus, as you say, the concern I have is for 'older' kit that is no longer in production. Although, again, I think of the stark contrast with 50 years ago when makers were happy and *proud* to give people diagrams, manuals, etc, as a sign of confidence in their work and customers, and to aid repairs, etc.
Given the rise in 'reuse, repair, etc' attitudes I wonder if this won't end up being mandated by goverments, anyway! It also helps avoid a problem I've encountered where a maker (*not* of hifi) was simply not willing to repair an item that was only three years old. *Despight* EU Law saying they were required to do this.