When calculating historical P/E and Dividend Yield Ratios for a company over the last 5 years, which date of the market price per share should I use?

My professor emphasized using the company's 10-K reports to find the data, and not using online databases to find TTM EPS, etc. As such, I am using the yearly earnings per share and dividends per share as stated on their 10-K forms. Their 10-K's show different dates for the end of their fiscal year, always ranging from late January to early February. However, I don't know which dates they are using to determine their reported EPS and dividends per share.

So, which market price per share should I be using to calculate these ratios? Should I just pick a standardized January 31st of each year? Or should I use their yearly average market price per share? Or would another date be optimal? Thanks in advance.