Why is my Roth IRA Cost Basis So Much Higher than my Contributions?

I just noticed that Schwab shows my Roth IRA Cost Basis as $85,000.  Primerica shows $56,000.  The thing is, these accounts started around 2000, and I was always contributing yearly, between the two accounts, such that I was making the maximum yearly contribution, and no more.  To have a combined Cost Basis across these accounts of nearly $140,000, that would suggest I have been contributing for well over 20 years. But that is not the case. So I can't make any sense of these reported figures on the schwab and primerica sites...