[BlueTemplar]

"Attributable" means by law enforcement, and mobile carriers, like all ISPs, must keep logs. In this case, for who had which IP address when.

(Otherwise, it's akin to the usual confusion between anonymity and pseudonymity.)

[chatmasta]

That’s true, but to be fair my original comment also said posts would be reliably associable with other posts from the same IP. With CGNAT, that association will be slightly less reliable, but not meaningfully so. The segment of the population who posts on 4chan is so low that there is negligible chance of two 4chan users sharing an exit IP and time window. Even with non-overlapping time windows, the population will be low enough for stylometry (and other factors) to remove any remaining ambiguity.