I'm reviewing a return with multiple pass-through K-1s.  in 2018, the taxpayer had excess business interest expense carryforwards from 4 different partnerships.  In 2019, only two of those partnerships show amounts on Sch A of Form 8990 in the prior year carryforward column.  I went back to the other two partnerships and noticed that they have no excess business interest expenses for 2019.  For the heck of it, I entered $1 in the box for excess business interest expense for one of these partnerships, and lo and behold, the partnership now appears on the F 8990 Sch A, with $1 current and the carryforward that I was looking for.  I'm not sure why I have to enter an amount in the current year to make the prior year carryforward appear in Form 8990.  I'm sure I'm doing something wrong, or not understanding this, but can someone help me?

Thanks!