My experience of IPR relates to software and matches John Halfpenny's comments. Unbelievably complicated! There used to be a few firms based in Switzerland who specialised in buying the rights to older software patents in hope of finding wordings that would allow them to demand cake from profitable vendors. Microsoft faced a number of challenges to their right to the Windows GUI, fought some in court, and I believe paid the Danegeld whenever going to law was risky. Often risky because juries are exceptionally thick when it comes to understanding anything technical!
Broadly though, IPR only matters if someone cares. No one cares if I photocopy a best-seller unless I foolishly boast about it on the internet, make copies available to others, or start selling them. However, steer clear of Thomas the Tank Engine, Harry Potter, and Disney characters because these and similar are protected aggressively on principle. Otherwise, the trigger seems to be the amount of money involved. Anyone earning worthwhile sums by exploiting someone else's IPR can expect to meet lawyers, trading standards officers, and policemen! If little or no money is being made, then the copyright owner might not care,
Gambling on the attitude of the copyright holder is a bit dodgy because only they know what they think. There will be trouble if they're planning to use the material themselves or are fed up with being ripped off and want to make an example of someone!
Older, forgotten and unfashionable IPR is safer than current expensive products. Copying is rather easy to do and mostty harmless. My golden rule is 'don't take the p*ss'.
Dave