Despite your knowledge on trading, have you been applying techniques of testing on better coins to trade in at that particular point in time? You may endeavor using the coin market cap, this avail you that opportunity to check where the particular coin is been ranked. Is it among the first 20? And stuff like that. You can also confirm at exchanges their value at that period in time. This however still considerend depend on the type of exchange.
The market cap is it really important? Because a friend of mine were saying I should always consider the usecase of any project before buying a particular coin. But even with that after much research about the project and I decided to buy, at last still sold at lost.