Flat 4A bells are standard on K5LA's nowadays. And they were fairly common even back into the late 70s. Even die cast bells tended to vary in pitch fairly dramatically from production line to the next up until the Micro-Precision era. All of this happening was most likely by chance.
The K5LA sound you mention was standard on GO Transit's first order of MP40's in 07-08 as well. https://www.youtube.com/watch?v=5DaCoUWHzKw
Here's another that's nearly identical on Coaster 2101.https://www.youtube.com/watch?v=91-4wGulwrg&t=75s
From the early 2000s to about 2009, this sound was quite run of the mill. Since most K5LA's from this era are oriented R24, and or are muffled behind a wall on a locomotive, and or sick and dying, you won't hear this particular sound often. I've tested a K3LA from this era, and believe it or not, the 4A was actually perfectly in tune. The 1 bell however was about 20 cents sharp, and the 2 bell was just 25 cents flat of a G note.
The first recording below is an Audacity combination with the notes at D#+20, G-35, G#+40, B, D#+20. As it would sound in the chord, the 2 bell would sound like it's 35 cents sharp, 3A would sound like it's 20 cents sharp, and the 4A would sound like it's 20 cents flat, thanks to the sharp octave. In the second recording, the only changes made are the 1 and 5 bells are flattened to a perfect D# octave. It really eliminates a lot of musical quality though. I heard both of these sounds on GO's MP40's.
The Micro-Precision K5LA's made today are similar to the second horn chord structure, except the 2 bell is now bored to around F#-25, and the 4A's, either by increased boring or minor changes in casting structure, now play around B-25.
The 90s K5LA sound that you would've heard fairly frequently on Metra up until a few years back is quite different. Back then, pretty much everything was sharp of the octave notes except for occasional flat 4A as mentioned earlier. The octave sometimes was sharper as well I believe. The additional 90s K5LA recording I made is more of a guess based on past information and not so much first hand experience. Sounds pretty accurate though. Of course, just like any era, there were plenty of different sounds in the 90s. This was just the most run of the mill it seems.
D#+35, G-35, G#+55. B+50, D#+35 are the notes in the recording.