dictionary.exists(key) ADDS the key - vba

Question

I am going crazy with VBA dictionaries, as the Exists() method makes no sense.
I thought you can use the dict.Exists(key) method to check if a key is in the dictionary without further actions. The problem is that when checking it, the key is automatically added into the dictionary. It really makes no sense!
Here's my code. Am I doing something wrong?
Function getContracts(wb As Workbook) As Dictionary
Dim cData As Variant, fromTo(1 To 2) As Variant
Dim contracts As New Dictionary, ctrDates As New Collection
Dim positions As New Dictionary, p As Long, r As Long
Dim dataSh As String, i As Long
dataSh = "Export"
cData = wb.Worksheets(dataSh).UsedRange
For i = LBound(cData) To UBound(cData)
fromTo(1) = cData(i, 1)
fromTo(2) = cData(i, 2)
Set ctrDates = Nothing
If IsDate(fromTo(1)) And IsDate(fromTo(2)) Then
If Not contracts.Exists(cData(i, 3)) Then ' Here it detects correctly that the key doesn't exist
ctrDates.Add fromTo
contracts.Add cData(i, 3), ctrDates ' And here it fails because the key just got added by .Exists()
Else
Set ctrDates = contracts(cData(i, 3))
ctrDates.Add fromTo
contracts(cData(i, 3)) = ctrDates
End If
Else
Debug.Print "Not a valid date in line " & i
End If
Next i
End Function

Answer 1

You can shorten your code to
For i = LBound(cData) To UBound(cData)
fromTo(1) = cData(i, 1)
fromTo(2) = cData(i, 2)
Set ctrDates = Nothing
If IsDate(fromTo(1)) And IsDate(fromTo(2)) Then
If Not IsEmpty(contracts(cData(i, 3))) Then Set ctrDates = contracts(cData(i, 3))
ctrDates.Add fromTo
Set contracts(cData(i, 3)) = ctrDates
Else
Debug.Print "Not a valid date in line " & i
End If
Next i
If one changes a value at a key it will automatically add the key if it does not exist.
Further reading on dictionaries
PS: This might also circumvent the strange behaviour described in the comments as you do not use the exist method. But on the other hand I have never experienced such a strange behaviour when using dictionaries

Answer 2

Collections of Date Pairs in a Dictionary
A reference to the Microsoft Scripting Runtime library is necessary for this to work.
Option Explicit
Sub GetContractsTEST()
Const dName As String = "Export"
Dim wb As Workbook: Set wb = ThisWorkbook
Dim dws As Worksheet: Set dws = wb.Worksheets(dName)
Dim Contracts As Scripting.Dictionary: Set Contracts = GetContracts(dws)
If Contracts Is Nothing Then Exit Sub
Dim Key As Variant, Item As Variant
For Each Key In Contracts.Keys
Debug.Print Key
For Each Item In Contracts(Key)
Debug.Print Item(1), Item(2)
Next Item
Next Key
End Sub
Function GetContracts(ByVal ws As Worksheet) As Scripting.Dictionary
Const ProcName As String = "GetContracts"
On Error GoTo ClearError
Dim cData As Variant: cData = ws.UsedRange.Value
Dim fromTo(1 To 2) As Variant
Dim Contracts As New Scripting.Dictionary
Contracts.CompareMode = TextCompare
Dim r As Long
For r = LBound(cData) To UBound(cData)
fromTo(1) = cData(r, 1)
fromTo(2) = cData(r, 2)
If IsDate(fromTo(1)) And IsDate(fromTo(2)) Then
If Not Contracts.Exists(cData(r, 3)) Then
Set Contracts(cData(r, 3)) = New Collection
End If
Contracts(cData(r, 3)).Add fromTo
Else
Debug.Print "Not a valid date in line " & r
End If
Next r
Set GetContracts = Contracts
ProcExit:
Exit Function
ClearError:
Debug.Print "'" & ProcName & "' Run-time error '" _
& Err.Number & "':" & vbLf & " " & Err.Description
Resume ProcExit
End Function

Answer 3

Possible Solution:
I had the same issue, this tends to happen when the compare more has not been set. I have not dug any deeper into this as the issue cannot always be replicated and the documentation around .Exists() and .CompareMode isn't that thorough source.
(as everyone has said you should enable the Microsoft Scripting Runtime reference for early binding)
When creating a new dictionary set its .CompareMode to vbBinaryCompare this will set a more strict compare mode and also in my case fixes the .Exists() bug. Do note that you can only set .CompareMode on an empty dictionary
Dim NewDictionary As New Scripting.Dictionary
NewDictionary.CompareMode = vbBinaryCompare
If NewDictionary.Exists(key) Then
'do things
End If