> They could have been bought by a bigger company.

Any acquisition (or bankruptcy) in the 2000s is highly likely to have created a web trail.

> If the copyright isn't registered, and often even if it is, there's no way to know who owns it now.

But trademarks need to be renewed, which creates a web trail. And companies that sue over things, have generally already filed suit (or been sued) at least once in their 30+ year history (assuming they still exist today), all of which creates a web trail.

Over my decades in the tech business, I've been fortunate to work with some excellent lawyers as my in-house general counsel and one of the best taught me an important meta-point about realistically evaluating the likelihood of getting sued. Because, no matter how unlikely, anyone can sue over pretty much anything. So after doing the likelihood calculation, remember to ask: "What would the plaintiff's damages be?" Let's imagine someone is crazy enough to spend many months or years and tens of thousands of dollars suing over this defunct, unknown software which hasn't sold a copy in 25 years. But, the law being the law, they win a judgement of damages amounting to a symbolic $1. Because the plaintiff has to prove the actions of the defendant caused them to lose some significant amount money - in the present tense. And making significant amounts of money selling software in the 2020s leaves a web trail.

Because crazy people exist, this bonkers $1 scenario has actually happened (although not in software preservation as far as I'm aware). And, in the rare cases where it's not thrown out by an irritated judge for wasting everyone's time, the judgement is a remedy ("stop doing that") and symbolic damages of $1. And, no, the defendant doesn't have to spend anywhere near what the plaintiff does to defend. You can get to default judgement by doing as little as just filing a few forms and having someone appear once. However, IF the company still existed - the far more likely scenario is they'd just ask OP to remove his blog post and that would be that.

The reason this point matters is that vintage software preservation is historically important yet unfortunately some of our IP laws were created with no thought for what happens in the 'abandonware' scenario where the product is long past economic viability (or even being able to be run) and the company is either gone or no longer cares.

It is always theoretically possible that someone objects to archiving and preservation but the consequences for an individual preserving the software for history and no financial gain, who took reasonable steps to find the copyright owner - are almost always nothing more than a C&D letter - and that's the rare worst case. This is based on decades of experience preserving copyrighted commercial abandonware by non-profit projects like Archive.org and MAME.

My concern is if enough people continually drop the pedantically correct drive-by warning "But you could be SUED" every time some volunteer preservationist saves another title from extinction, people who don't understand there's virtually zero chance in a case like this that OP suffers any meaningful harm simply won't do volunteer preservation or help those who are. It's a form of concern trolling which doesn't help while potentially causing a good thing to happen less.