Sharepoint Cascading Dropdowns - Show Default Value from List B in List A

I have a sharepoint list setup for employees to make reservations for a training session. There is also a linked list where count against each session is updated when someone books a session, which has been completed using Nintex Workflows. So in effect:

List A Cols Staff Name - Session Details

List B Cols Session Details - Session Booking Count

What I am trying to do is have the Session Booking Count shown on newform of List A if user selects a specific session, and to write a validation to show error if Count > 10.

I have tried to setup a cascading dropdown option using jquery, and this does show the count of each session, however default value is coming as "(none)". User has to click on the drop down and select the count figure manually.

Is there a way to change this so that by default the count is shown?

The sharepoint I use does not have SPD or Infopath.