How do I determine taxable amount on each of two CSRS 1099-R's?

I have a survivor annuity 1099-R and a "regular" annuity 1099-R. Both say "UNKNOWN" in the taxable amount box. After doing the "simplified method" calculation for each, an amount is shown for each being "tax free amount previously recovered." I can't get my head around what that means. Do I subtract that "tax free recovered" number from the total distribution to get the taxable amount?

Also the program filled in the full amount of distribution as taxable for the surivor. And left the other (regular annuity) taxable amount empty. (The entire distribution shows taxable on the IRS form for the survivor and remains "unknown" for the other.) HELP!!

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