Need to make an incrementing Customer ID in Access without Autonumber - mysql

Question

I am currently creating a database for our company and I would need to add a Customer ID to each new record.
I designed a data entry form and have the following Module running on it to create the ID:
Option Compare Database
Function NewCustomerIDCode() As Long
Dim db As Database
Dim LSQL As String
Dim LUpdate As String
Dim Lrs As DAO.Recordset
Dim LNewCustomerIDCode As Long
On Error GoTo Err_Execute
Set db = CurrentDb()
'Retrieve last number assigned for Customer ID Code
LSQL = "Select Last_Nbr_Assigned from CustomerIDCode"
LSQL = LSQL & " where Code_Desc = 'Customer ID Code'"
Set Lrs = db.OpenRecordset(LSQL)
'If no records were found, return an error
If Lrs.EOF = True Then
LNewCustomerIDCode = 0
MsgBox "There was no entry found in the Codes table for Customer ID Code."
Else
'Determine new Customer ID Code
LNewCustomerIDCode = Lrs("Last_Nbr_Assigned") + 1
'Increment Customer ID Code in CustomerIDCode table by 1
LUpdate = "Update CustomerIDCode"
LUpdate = LUpdate & " set Last_Nbr_Assigned = " & LNewCustomerIDCode
LUpdate = LUpdate & " where Code_Desc = 'Customer ID Code'"
db.Execute LUpdate, dbFailOnError
End If
Lrs.Close
Set Lrs = Nothing
Set db = Nothing
NewCustomerIDCode = LNewCustomerIDCode
Exit Function
Err_Execute:
'An error occurred, return 0
NewCustomerIDCode = 0
MsgBox "An error occurred while trying to determine the next Customer ID Code to assign."
End Function
The problem is, if for example someone starts entering data in this form an ID is assigned (example: 1023). If for any reason they decide not to finsh the entry and delete the record, the next entry will get number (example: 1024). But I would need 1023 to be reused because it is not linked to a record. For accounting reasons I cannot have this number skip.
On the other hand if the new record is created and for whatever reason is deleted in a year, it's number cannot be reused. For example we delete record 1023 but our last entered record is 1145 the next record should get 1146 and not the deleted n° 1023.
Just for some background info I have a separate Autonumber for the primary key. This is not visible to users and has no meaning to the record except for Access to have a unique number for each record.
Can someone help? I've been searching the net for a day and the only stuff I can find is about autonumbers which does not apply here.