Since everyone who was quick to conclude and judge that Exo Ko Ko Bop's streams were fake and fan manipulation, was extremely slow or hesitant to provide actual legit proof for those conclusions/accusations/rumors, I decided to do some googling myself.
Since I'm no EXO-L, and only paid superficial, fleeting attention to those matters spoken of back then.
This is what I've found so far:
The only times Melon announced their chart reforms that I found
* (early) July '17: Melon system reformation (artists barred from releasing songs at midnight)
* July '18: chart freeze from 1-7 AM (Melon and other charts, in response to sajaegi)
* July '20: change to the 24h chart
When it comes to EXO and Melon:
EXO’s ‘Ko Ko Bop’ scores the 2nd Highest amount of Unique Listeners by any artist on Melon during the first hour after the system change that barred any artist from releasing music at midnight.
- EXO, which is usually just known for its physical album sales, became the first idol group after the chart change to debut at number one on the Melon chart, arguably the most popular chart in Korea, with “Kokobop”
On October 18, Hanteo chart apologized for manipulating EXO's 2017 Album sales. They officially admitted that their employee manipulated EXO's album sales and Chinese bulk order numbers with an intention to show less count of sales.
In the apology letter, Hanteo wrote "We apologize to our customers for what happened on August 17, 2017. Our official apology was delayed as we felt troubled over how to express our apologies." In short Hanteo expressed "We do not favor any artist and treats every artist equally. The incident happened due to a mistake by an employee. All purchases which are made through lawful platforms will be reflected on Hanteo charts. We will continue to work hard to provide a fair and trustworthy platform."
On August 17, 2017, Hanteo staff member made an announcement that the Chinese group orders wouldn’t be counted towards album sales and this caused a huge issue. EXO's Chinese fan base sent a message to Hanteo explaining how this is unfair and is an act of racism/discrimination. Later Hanteo made a statement that it was a mistake by an employee and posted an apology.
This was not the first time EXO was subjected to such unfairness. In 2016, Melon music awards denied an award which rightfully belonged to EXO. When fans demanded an explanation from the show conductors, they simply stated it was due to "Internal data".
But on October 2017, Melon released the details of most streamed song in 2016, and it was EXO's Monster, with 190,898,389 streams.
Granted, this was just a quick browse and look up, so maybe I missed some.
But these were the actual, announced Melon (and other charts) changes that I could find so far.
They were either before EXO's Ko Ko Bop release, or a very long time after.
The reasons given for those changes were also all kinda different stuff, the only times that EXO got mentioned in relation to Melon charts and changes was that they were doing so well despite the chart changes (or that they'd been unfairly treated/robbed).
Like said, I might've missed some announced Melon chart changes. If so, I'd like to invite those making the quick judgements and rumor repeaters to provide the evidence that states Melon changed because of EXO's Ko Ko Bop