concatenate text box from combobox text box and add next available number to last concatenation

[energistics]

Hey guys,
Please help. I'm trying to concatenate a text box in my access form. It takes the second column of the combo box named cmbType and adds a dash then the second column from a second combo box (cmbStation) and adds another dash and then im stuck.
The last concatenation needs to be a total of the types available from the types query which is queried from the fist combo box. So selecting the fist combobox queries the types query based on the selection of the first combo box. So I can take
that total number and concactenate it to the last section of my concatenated text box. that works great only when adding a new record but when updating any record say record 1 the text concatenation does not show the last concatenation
sum of the query. I want to be able to keep the assigned number or the last assigned number on the txt box concatenation so that when i update the record it keeps the last concatenation and only updates the parts that need updating on the txt box.
Any help is appreciated
Energistics