Can someone please point me to where I can find the historical rates that must be applied to mandatory employee contributions in DB plans?

I'm looking for the mandatory interest rate on employee contributions that was in effect in 1988. I’m pretty sure it went to the current rule of 120% mid-term AFR in 1990, and I think it was 5% early on, but I also think there was another iteration of the regs between the 5% rule and the 120% rule.

I apologize if I should be able to find this information elsewhere on this site.

Thanks.

IRC 411©(2)©(iii). 5% established by ERISA. Changed by OBRA87 to 120% of mid-term rate, effective for plan years beginning after 12/31/1987.

This site has AFR rates going back to 1996: http://www.timevalue.com/afrindex.htm