I am in agreement with you on the phrasing "ability to recall/recollect the event". You might notice that I left out "the event" in my analysis. Your phrasing on the Ruin issue is far better than I was coming up with on short notice, so I avoided it.
And thank you for the page number; that got me back to the scene far faster. I had been thinking more about the portion where Sazed is actively storing as he enters the Conventical.
The ability to recall a visualization degrades very quickly, so he mentions having to store it very directly; he uses this technique on a pillar. Most of his storage during the scene is combined visual and vocal descriptions of the environment. He does vocalize a few other cues, like how the steel floor is cold underfoot. He casually discards the idea of a photo-style memorization of the writing in the basement, noting that "no man could stare at a wall of so much text, then remember the words." [pg 133, PB]
It is hard to say if a Feruchemist can strip a person out of a scene, though storing the audio of a meeting should be easy enough. But would you end up storing just the audio, or would associated body language and other closely tied factors be stored as well? It is hard to define the unit size of a memory.
However, would a Copper Compounder be able to burn a visual memory of the plate back into his head in such a way that he could read the words? Would this make the memory so tightly associated in his head that he couldn't forget it (without storing it again, at least), or does compounding simply increase your ability to recall the item to a level far beyond normal that will take far longer to decay? And does this distinction have any real meaning?
Most likely, a compounded visual memory will be readily recalled for several years after the burn-in, while faces and conversations could last many decades after burn-in. A dramatic, emotional event would become unforgettable (it may already have been, after all).
Specific burn-in durations would depend on the strength of recall at time of storage, how fast your normal decay rate for that type of memory is, and how much you use the memory afterward. For example, I naturally forget names told to me within approximately two hours, so compounding would possibly get me a few months of solid recall. As long as I am around the person at least few more times during those months (or I compound the memory again *hint*), I should not have trouble recalling the name for about a decade. On the other end of the spectrum, I recall anything I read very accurately for months or even years in some cases, so compounding fresh memories of a book's text would probably allow me to recite the book at will; I'd die of old age before it would noticeably decay.