If the boundary can not be planted, we will put TT (no mark) in the plan & field book. How about in e-submit?

In the e-submit program, there are 2 categories-front and back. what it means?

In the e-submit program, there are 2 categories-front and back. what it means?
In above case, I have planted marks 20 (pkB) and 24 (pB) from stesen 1. How I going to define point 28 (TT)?
In e-submit program, it do not allow to key data by 20-28 or 24-28. Please kindly assist me. My dear friend.
Tq.