I'll add a few observations:
IMO pins are forced into the chain outer plate holes, "force" here to mean they don't enter the plate due to the force of gravity alone. Yes there is a range of "force fit/slip fit/interference fit" but I doubt most here have the experience, education or tooling to measure the forces along this range let alone claim that at some point the term changes from interference fit to force fit. If I'm wrong of readers having the equipment to measure this stuff I am all eyes and ears to learn more. But as we should all know modern derailleur gear systems can (and due to poor rider skills) and do get shifted under tremendous loads as seen by the teeth and links. So even a non deforming pin fit to the outer plate has been shown to not be able to retain the plate on the pin end under there loads. Shimano (Not sure if they are the original designer or they just bought into the design) came up with the idea of peening over the pin ends to create a lip to better capture those outer plates. This peening comes in varying amounts and the amount is usually indirectly refereed to as "strength of chain". This peening can and does create a larger hole in the outer plate if the pin were to be removed, or if a pin was already peened before installation. It is this last bit that drove Shimano to come up with the UG assembly pin. It has a disposable pilot shaft that also has a ramp at it's end by the portion of the pin that will remain in the chain. This assembly pin has a slightly larger diameter then the original pins have and the ramp better allows the install of this pin without further plate hole damage. I do know nothing has been said about the chain's earlier assembly onto the bike.
I have seen the results of what was explained to me as cleaning products caused cracking before too, just not common. That Super Agitene I mentioned would discolor Regina Oro chains if left to soak over night. The brassy colored outer plates would become silver colored. NOT what your customer who paid your price for that chain wants to find out when they pick the service job up...
While outer plate cracking is not a common issue there have been production errors that weren't caught till thousands of chains made their way to the market. The (IIRC) late 1980s saw Sedis (prior to their molding into SRAM) have a number of SedisSport (or the equivalent model for that year) chains suffer from cracking outer plates. I had a chain crack on a tandem we rode and I've seen a few more at work too. It was fairly well known in the LBS world back then. The story I heard was embrittlement from less than right heat treating. I have seen a few other brand and model chains crack at the pin holes over the years but as others have said it is not a common failure mode.
Much more common is a "mechanic" reassembling the chain without aligning the two outer plates so that the pin tries to enter the far hole off center. A small chain pin tool has way more then enough strength to deform that outer plate beyond safe use. This I have seem many times, less so in the last 10ish years as connecting links have become the home assembly method of choice. This thread is not about that though.
Another interesting experience I've had, unrelated to chain cracking but involve heavy rust, was back in the later 70s I had a Raleigh Twenty (not the DL-20) that I had fitted a SA FW . This was to be my ride to work in the winter bike, which I did a couple of times and really didn't like the slushy riding we have here. Away went the bike till summer and low and behold the chain was so rusty I could almost hold it out straight. I solvent cleaned it at work (Super Agitene) which did nearly nothing to the rust or to freeing up the links. Wire brushed off the outsides best possible. I worked the chain link by link till there was enough pivoting freedom to remount the chain. Oiled and tensioned the chain best possible knowing I would be removing it soon to again clean it out. Rode it to and from work for a few days, a flat 1.5 miles one way. When I was to remove the chain for the follow up cleaning I noticed it was drooping as though the wheel had slipped in the slot (those SA nuts do like to strip out their threads on the hardened and flat spotted axle)I flush out the chain and saw the rust was nearly all gone. The wear surfaces were shinny and only very light spec rust remained on the non critical surfaces. Reinstalling the chain showed the wheel was still well secured but now about 4ish mms too far forward for the right chain tension (which we all know that for a SA IGH is no tension
. That was how much space the rust had taken up in each link adding up to the "longer" chain after abrading off the rust in that week of riding. Andy