The DSM isn't the only book, and is not the singular source of diagnosis around the world, so believing that because CPTSD is not in the DSM and therefore doesn't exist is also disingenuous.

The ICD does have an entry for Complex PTSD, but it may not match what many people think of as CPTSD, which from what I see is closer to what Bessel van der Kolk called "developmental trauma."