Carry Forward Values until Change

You're Right, that did fix it, but for some reason its still not populating the blanks with 1.1404

Heres the code:

Filled Value = 
VAR _LNB =
    CALCULATE (
        MAX ( '3. RATES_TABLE_MMMF'[Date] ),
        FILTER (
            '3. RATES_TABLE_MMMF',
            '3. RATES_TABLE_MMMF'[Date] <= EARLIER ( '3. RATES_TABLE_MMMF'[Date] )
                && '3. RATES_TABLE_MMMF'[Unique key] = EARLIER ( '3. RATES_TABLE_MMMF'[Unique key] )
                && NOT ISBLANK ( '3. RATES_TABLE_MMMF'[Daily_Rate] )
        )
    )
RETURN
    CALCULATE (
        MAX ( '3. RATES_TABLE_MMMF'[Daily_Rate] ),
        FILTER (
            '3. RATES_TABLE_MMMF',
            '3. RATES_TABLE_MMMF'[Date] = _LNB
                && '3. RATES_TABLE_MMMF'[Unique key] = EARLIER ( '3. RATES_TABLE_MMMF'[Unique key] )
        )
    )

Whcih field sets the Rate? I'm going to do in Power Query which is much mor efficient for these types of tasks

The rate is brought into the table via a related forumla based on the uniuqe Key

So the values have to be filled in based on date and Unique key?

Thats correct, the Unique Key is essentially the Month/Year/Code that connects to a 1:1 match with a Rate table. This case here, there was no entry for August, because the rate was unchnaged from July. so the result is all blanks until the rate chaged in September

See if this code in Power Query works for you:

let
  Source = Excel.Workbook(
    File.Contents("D:\OneDrive\1 Shared web\Comm PBIs\Filled Value\Power BI\Book2.xlsx"),
    null,
    true
  ),
  Sheet1_Sheet = Source{[Item = "Sheet1", Kind = "Sheet"]}[Data],
  #"Promoted Headers" = Table.PromoteHeaders(Sheet1_Sheet, [PromoteAllScalars = true]),
  #"Changed Type" = Table.TransformColumnTypes(
    #"Promoted Headers",
    {
      {"Date", type date},
      {"Unique Key", type text},
      {"DAILY_RATE", type number},
      {"RT_RATE_INDEX_CCY", type text},
      {"DAILY_TABLE_KEY", type text}
    }
  ),
  #"Sorted Rows2" = Table.Sort(
    #"Changed Type",
    {{"RT_RATE_INDEX_CCY", Order.Ascending}, {"Date", Order.Ascending}}
  ),
  #"Duplicated Column" = Table.DuplicateColumn(#"Sorted Rows2", "DAILY_RATE", "RATE"),
  #"Group" = Table.Group(
    #"Duplicated Column",
    {"RT_RATE_INDEX_CCY"},
    {{"All_Rows", each Table.FillDown(_, {"RATE"}), type table}}
  ),
  #"Expanded All_Rows" = Table.ExpandTableColumn(
    Group,
    "All_Rows",
    {"Date", "Unique Key", "DAILY_RATE", "RT_RATE_INDEX_CCY", "DAILY_TABLE_KEY", "RATE"},
    {"Date", "Unique Key", "DAILY_RATE", "RT_RATE_INDEX_CCY.1", "DAILY_TABLE_KEY", "RATE"}
  ),
  #"Changed Type3" = Table.TransformColumnTypes(
    #"Expanded All_Rows",
    {{"Date", type date}, {"RATE", type number}, {"DAILY_RATE", type number}}
  ),
  #"Reordered Columns" = Table.ReorderColumns(
    #"Changed Type3",
    {
      "RT_RATE_INDEX_CCY",
      "Date",
      "Unique Key",
      "DAILY_RATE",
      "RATE",
      "RT_RATE_INDEX_CCY.1",
      "DAILY_TABLE_KEY"
    }
  )
in
  #"Reordered Columns"

New file attached

Thank you so much for your continued help! the data I sent earler was a cut out of my overall model. In my model, my data is being retrieved from an oracle database and the table I provided is the result of a daily table:

3. RATES_TABLE_MMMF = 
    Var Cal = 
    CALENDAR(DATE(YEAR(TODAY())-1,1,1),max('PS_RT_RATE_TBL'[EFFDT]))
    Var Des = 
    SUMMARIZE('PS_RT_RATE_TBL',PS_RT_RATE_TBL[RT_RATE_INDEX_CCY])
    VAR TAB = GENERATE(Cal,Des)
    Return
    TAB

Other columns:

DAILY_RATE = RELATED(PS_RT_RATE_TBL[RATE_MULT])
Unique Key = MONTH([date])&YEAR([date])&[RT_RATE_INDEX_CCY]
DAILY_TABLE_KEY = [DATE]&[RT_RATE_INDEX_CCY]

How may I adapt your code to these paramaters? 

The Power Query method need the tables in Power Query, and Calculated tables are no accesible in PQ . So we need the imported 

'PS_RT_RATE_TBL'

to be able to build the whole table  in PQ instead of using DAX