Retirement tax questions

Ah, makes sense. Since my CB has not been tracked thus far, I see no way to accurately start now, and I am over 60. The only value would be in what dmertz said .. to possibly deduct unrecoverable loss in future. My Roth is comprised of 5 years of conversions and 2 rollovers. You'd think I could retrieve an accurate cost basis ? I could try. Please Advise