I think the "out of print" argument is a cop-out. That's allowing the economic constraints of physical copy production to override the ideals behind the law.
Things went out of print because the unit cost of producing one extra copy was much higher than producing 10000 extra copies. As demand for copies tends to taper off over time, you eventually reach a point where you simply cannot produce just one extra copy at a cost lower than the price the next customer would be willing to pay for it.
No such pressure exists for digital reproduction. Every additional copy costs the same low, low amount. The author then has no reasonable argument for refusing to make an additional copy.
And yes, there was infrastructure for capturing and preserving copies of print flyers. It wasn't all-encompassing, and didn't catch everything, but there are many museums of ephemera now that have extensive collections of published material that was of limited circulation (and limited literary value). For those items that were expected to get thrown away or used as toilet paper, there was always the possibility that someone might have saved it, and it could still be around in some form 200 years later.
It is entirely reasonable for an author to demand that no one else make and distribute copies of their work. But in my opinion, if you can find the author, and make them a reasonable offer for a new copy of their copyrighted work, and they refuse to make one and sell it to you (or to license the right to make your own) then they have essentially abrogated their copyright. You would then be morally (but not legally) justified in copying that work from another source.
When something is published, the genie is out of the bottle. No law can stuff it back in. And copyright was intended to protect the livelihoods of creators, not to give them the ability to more easily destroy what they have wrought. Thus, whenever there is any confusion or ambiguity, I always personally interpret a copyright situation with the test "is there any way this might lessen the creator's ability to sell (or otherwise monetize) one more copy of this work?"
If the creator is no longer attempting to make money from a work, screw their copyrights. We granted them that limited monopoly to make enough money so that the effort of creation would be worthwhile to them. If they don't care to sell, I don't care to protect their ability to sell exclusively.