I didn’t have time to explore the page much but I noticed a small wording issue that I figured you’d want brought to your attention:
The sentence “A book how to make your forms better.” is missing the word “about” (alternatively, “A book” can be replaced with “About”).
I left my tenure at Google with this same impression. Data is constantly being copied, denormalized, cached and transformed. It is true that efforts are made to leave an audit trail that could in theory be followed from initial source data to all derivatives. However, this is practically infeasible and certainly not doable with a single engineer’s worth of knowledge about the system.