Historical fundamental data are easy for a stable company until it's not stable.
Spinoffs, mergers, company restructures, change of domicile, change of reporting currency, change of fiscal year boundaries, significant change in company operations. How about tracking stocks? What about restatement of sketchy previous financial reports? Also consider companies that provide staggered reporting of their fundamentals (we'll tell you earnings per share and a few other things, but you have to wait 4 weeks for the rest buddy, because we're still cooking the books).
I have no idea how you'd handle a company like Liberty that seems to create tracking companies about twice a year for some portion of their company that nobody understands. Look at their latest garbage with GCI Liberty.