Auditor, and very soon to be CPA, here. The author "downloaded quarterly accounting data for all firms in Compustat, the most widely-used dataset in corporate finance that contains data on over 20,000 firms from SEC filings." Quarterly reports are unaudited by an independent CPA firm (most often KPMG, PWC, EY, Deloitte), while annual reports (10-K) are audited. I would be curious if the the sum of squares analysis is as significant in the latter set.