Unless, I am missing something, you already have the cost basis for each of your coins in the spreadsheet because you mention you have this information. Your cost basis for each coin remains the same no matter how many transactions you make.
For the missing information for the two coins, use the purchase price and fee in the spreadsheet for each transaction. If you are summarizing and combining transactions, your solution should work. Be as specific as possible and summarize your calculations in a well-written statement in case if the IRS has questions about it. As the old adage goes, "Be prepared for the unexpected".
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