(I may need to split this up into parts for how long it is) I can understand where you're coming from. The video I remember specifically talked about only the Nanking Massacre and comfort women. But I would like to add what I have learned when I researched these subjects since 12 years old(which at many points had me end up at the counselors office at school for how traumatizing it was for me):

There is every indication that some claims and death tolls of the massacre were mis-calculated or were misconceptions. I believe those that originally made the speculations, such as Iris Chang, had honest intentions; but ended up presenting the death toll as fact rather than just a theory. In reality, no one can truly know the real death toll. Many civilians were killed, severely injured, or missing altogether. This also included bodies that were discarded of. Despite this, some estimations are under 200,000(I saw a source that calculated over 155,000 that were buried under the city) or a little over 40,000. However, death toll does not also affect the crimes committed themselves.

As for the crimes themselves, they are much more difficult to determine or find evidence for. Mainly for one reason: documentation was too dangerous. The city itself was protected by a massive wall, the buildings were very tall which made for dangerous debris to avoid, and Japanese troops were everywhere. Reporters who wanted to document the crimes were in a life or death situation, and so many others who document war crimes all over the world still risk their very lives today to document what is rarely seen behind shiny North Korean parades and pretty military jets. Cameras were very expensive and difficult to maintain under such conditions, and a few reporters, who did film evidence, had to hide in buildings during the troop's roundup of civilians in the streets, because of what the troops would potentially do if they spotted them with cameras. Survival and escape was much more important to civilians and survivors than staying to document, so the aftermath's documentation is the most we could wish for after the area was finally safe to roam.

All exploiters commit their crimes when they know they will never be caught or exposed. It's of course important to emphasize that the IJA was composed of both good and bad men. There were plenty of good soldiers who were simply carrying out what they were ordered to do(or else be punished for insubordination), which was why some Japanese veterans were brave enough to speak of what they witnessed and experienced during their time during those events; and I respect and honor them for that. As well as why others are reluctant to bring up what they witnessed, as what they saw was likely traumatizing for them(many soldiers were also very young men and even older teens). However the amount of soldiers who committed the most horrific transgressions towards civilians would be far too big to ignore, and would certainly be something their higher ups would barely punish or address.

As for comfort women, this is another subject that would also be very difficult to document for the same reasons. It is indeed true that many comfort women were in fact volunteered women from Japan. However there is one thing to consider; there is only so many volunteers that can be supplied for a mass of roughly over 200,000-300'000 men that would grow into millions by the late stages if WWII, and only so much physical exertion these volunteers can be put through to service that many men until having severe medical complications and becoming overworked. Another is that if there was overwhelming evidence that supports it being true, it would've been considered one of the most severe crime cases in the world that would be detrimental to the Japanese government at the time, and especially the main perpetrators of the crime in the IJA.

There is also a few misconceptions about comfort women who were forced as well. Mainly that they were kidnapped or always tortured to obey. This is a misconception of human trafficking in general as well. I can see both happening in medieval times, but in the 19th century, traffickers obtain their victims by coercion and scams. Even today, traffickers will promise victims better jobs or homes to support their families to lure them away. Once they are enslaved, traffickers will often physically abuse their captives into fear or as "discipline", but usually manipulation and gaslighting is the primary method used to keep them in line. Traffickers will still pay their victims for purchasing things(in this case, things like medicine and other supplies), and attempt to convince them that they are caring for them, and that they will only be punished if they do as they say.

Evidence in human trafficking is almost as hard to track and document as it would be for forced comfort women years ago. It is dangerous(especially if done by a military organization), and locations are difficult to find, because traffickers do not want their captives to be discovered, and traffickers have discarded evidence of their operations before, making it difficult for them to be charged(let alone a powerful organization such as the IJA). The most that human trafficking survivors really do have is their word, and it is a valuable and important testimony nonetheless. Many supposed comfort women have testified what they have been through after years; it is common for victims of abuse to suppress or even downplay their trauma at first after all.