data management system using userform

Hi, Im trying to make a data management system based in excel, and i have alot of questions that needs help with. Previously, i tried making individual example workbooks and posting a new thread for every question that i have. In the end, because every answer is tailored to each specific question, i had a hard time trying to combine them together in the actual workbook. So now im posting the workbook that im working on so that anyone who wants to help has a clear picture of where im going.

Maybe i will start by asking this question:
in the userform under "Sample manager" tab, combobox7 takes data from sheet "Case Log" column A. What i hope to achieve in combobox8 is that it populates only with values that contain 2 hyphens. For example, user selects DVI-00001 in combobox7, combobox8 should only show DVI-00001-001 and DVI-00001-002 instead of including DVI-00001-001-1 and DVI-00001-001-2.

Attached workbook for reference (file is over 2MB so had to compress it)