Well, after considerable effort I found this article from 2016 related to the retired version 14.12. Works in 18.12. It appears the Design Team needs to spend more time with the Development Team. The UI should have a Delete button, perhaps, near the Save - Return buttons. With all the improvements to SQL version, there are still many frustrations in the UX. 

This is what the link shows: 

• Can you delete a Company or Person (Contact) from the Address Book Estimating Management Console (EMC)?
• How to delete a Company or Person (Contact) record from the Estimating Address Book

To delete a record:You can either delete a record in the address book or make it inactive. When marking a Company or Person as Inactive, they will not appear in selection lists.

1. Open the Address Book
   • In Estimating, Click the File menu button , then click Address Book
   • In the EMC, click the Address Book tab.
2. Expand either the Company or People list, depending on which record you wish to delete
3. Select the company or person record by clicking on it in the Companies/Contact list pane 
4. Press the Delete key on your keyboard
5. This action cannot be undone and the record will be permanently deleted so you will need to click Yes to confirm.

To mark a Company as inactive:

Option I: In the Address Book

1. Open the Address Book
   • In Estimating, Click the File menu button , then click Address Book
   • In the EMC, click the Address Book tab.
2. Expand either the Company or People list, depending on which record you wish to delete
3. Select the company or person record by clicking on it in the Companies/Contact list pane 
4. In the record detail pane on the right, find the Inactive checkbox
5. Place a checkmark in the box and click the Save button

Option II: While editing an estimate

1. In any cell which allows Address Book access, click the  button
2. Select the Company you wish to deactivate Click Edit Selection
3. In the record detail pane on the right, find the Inactive checkbox
4. Place a checkmark in the box and click the Save button

Note: In earlier versions of the Microsoft SQL version of Sage Estimating it was not possible to delete individual records from the Address Book. Use the Inactive checkbox instead.

Well, after considerable effort I found this article from 2016 related to the retired version 14.12. Works in 18.12. It appears the Design Team needs to spend more time with the Development Team. The UI should have a Delete button, perhaps, near the Save - Return buttons. With all the improvements to SQL version, there are still many frustrations in the UX. 

This is what the link shows: 

• Can you delete a Company or Person (Contact) from the Address Book Estimating Management Console (EMC)?
• How to delete a Company or Person (Contact) record from the Estimating Address Book

To delete a record:You can either delete a record in the address book or make it inactive. When marking a Company or Person as Inactive, they will not appear in selection lists.

1. Open the Address Book
   • In Estimating, Click the File menu button , then click Address Book
   • In the EMC, click the Address Book tab.
2. Expand either the Company or People list, depending on which record you wish to delete
3. Select the company or person record by clicking on it in the Companies/Contact list pane 
4. Press the Delete key on your keyboard
5. This action cannot be undone and the record will be permanently deleted so you will need to click Yes to confirm.

To mark a Company as inactive:

Option I: In the Address Book

1. Open the Address Book
   • In Estimating, Click the File menu button , then click Address Book
   • In the EMC, click the Address Book tab.
2. Expand either the Company or People list, depending on which record you wish to delete
3. Select the company or person record by clicking on it in the Companies/Contact list pane 
4. In the record detail pane on the right, find the Inactive checkbox
5. Place a checkmark in the box and click the Save button

Option II: While editing an estimate

1. In any cell which allows Address Book access, click the  button
2. Select the Company you wish to deactivate Click Edit Selection
3. In the record detail pane on the right, find the Inactive checkbox
4. Place a checkmark in the box and click the Save button

Note: In earlier versions of the Microsoft SQL version of Sage Estimating it was not possible to delete individual records from the Address Book. Use the Inactive checkbox instead.