Arguably this is already true of text. We have already entered the age where it is impossible to determine with certainty whether a blog article was written by a human, and so every text data set that includes 2023 internet data will include ChatGPT outputs as ground truth.
Future historians will likely place a great deal of emphasis on 2019 being the year in which we reached a forever-maximum of non-pandemic-tinged provably-human-created data. It's no reason to panic, and the mixed data sets will absolutely be representative of humanity's accomplishments as a whole... but there will be notable differences.