...
NOTE: After you have added a model you will need to restart NAPA in order for it to be selectable in dropdowns etc. If you added it for another user, they must also logout and back in to get the new data.
The Product Model window holds more data than Product Make.
...
You will want to set Class to the class that the model belongs too, note there are more rows than originally displayed in drop down (although no scroll bar is showing)
Make it Current and set MOD Eligible to All MODS and Eligible to Y.
If this aircraft belongs to a Series, you will need to find the Model Seqnum of the series to put the value into Prod_Mdl_Series_Seqnum. (Example below)
You will need to Exit the application and go back in to get the Models added into the Product tabs/drop downs.