Aggregating Historical Data

I have X number of previous months data with a computer name, model, serial number, last online date.

January

A , laptop a  , 2ac  , 1/17/17

B , laptop a  , 5ga  , 1/27/17

C , laptop b , n3f  ,  1/31/17

February

A , laptop a  , 2ac  , 2/22/17

B , laptop a  , 5ga  , 2/27/17

D , laptop b , k3a  ,  2/28/17

March

E , laptop a  , 2ac  , 2/22/17

F , laptop a  , 5ga  , 2/27/17

D , laptop b , k3a  ,  2/28/17

Result:

A , laptop a  , 2ac  , 1/17/17 , 2/22/17 , null

B , laptop a  , 5ga  , 1/27/17 , 2/27/17 , null

C , laptop b , n3f  ,  1/31/17,       null   , null

D , laptop b , k3a  ,      null   ,  2/28/17, 3/28/17

E , laptop a  , 2ac  ,     null    ,       null  , 3/22/17

F , laptop a  , 5ga  ,     null   ,       null  , 3/27/17

I want to do this operation to the data:

If the computer name exists in the previous month (left table), add a column called "last online date.1" from (right table) "last online date."

If the computer name does not exist in the previous month (left table) add a new row from the new month (right table) to the (left table).

On the next join I want to add "last online date.2" if the computer name exists, and continue to add a new row if it doesn't.

This was the best way I could hack the data together to at least have something to look at but it is unsustainable:

let
    Source = Table.NestedJoin(#"Inventory2017-1-3 2-35-15-360",{"Computer Name"},#"Inventory2017-2-14 2-35-11-769",{"Computer Name"},"Inventory2017-2-14 2-35-11-769",JoinKind.FullOuter),
    
    #"Expanded Inventory2017-2-14 2-35-11-1" = Table.ExpandTableColumn(Source, "Inventory2017-2-14 2-35-11-769", {"Last Location", "Computer Name", "Last Checkin", "Status", "Computer Model", "Serial Number", "User ID"}, {"Last Location.1", "Computer Name.1", "Last Checkin.1", "Status.1", "Computer Model.1", "Serial Number.1", "User ID.1"}),
    Mergelocation = Table.FromRecords(Table.TransformRows(#"Expanded Inventory2017-2-14 2-35-11-1", (r) => Record.TransformFields(r,{"Last Location", each if r[Last Location] is null then r[Last Location.1] else r[Last Location]}))),
    Mergecname = Table.FromRecords(Table.TransformRows(Mergelocation, (r) => Record.TransformFields(r,{"Computer Name", each if r[Computer Name] is null then r[Computer Name.1] else r[Computer Name]}))),
    Mergestatus = Table.FromRecords(Table.TransformRows(Mergecname, (r) => Record.TransformFields(r,{"Status", each if r[Status] is null then r[Status.1] else r[Status]}))),
    Mergemodel = Table.FromRecords(Table.TransformRows(Mergestatus, (r) => Record.TransformFields(r,{"Computer Model", each if r[Computer Model] is null then r[Computer Model.1] else r[Computer Model]}))),
    Mergeserial = Table.FromRecords(Table.TransformRows(Mergemodel, (r) => Record.TransformFields(r,{"Serial Number", each if r[Serial Number] is null then r[Serial Number.1] else r[Serial Number]}))),
    Mergeuser = Table.FromRecords(Table.TransformRows(Mergeserial, (r) => Record.TransformFields(r,{"User ID", each if r[User ID] is null then r[User ID.1] else r[User ID]}))),
    #"Removed Columns" = Table.RemoveColumns(Mergeuser,{"Last Location.1", "Computer Name.1", "Status.1","Computer Model.1","Serial Number.1", "User ID.1"}),

    #"Merged Queries" = Table.NestedJoin(#"Removed Columns",{"Computer Name"},#"Inventory2017-3-14 2-35-10-828",{"Computer Name"},"Inventory2017-3-14 2-35-10-828",JoinKind.FullOuter),
    #"Expanded Inventory2017-3-14 2-35-10-828" = Table.ExpandTableColumn(#"Merged Queries", "Inventory2017-3-14 2-35-10-828", {"Last Location", "Computer Name", "Last Checkin", "Status", "Computer Model", "Serial Number", "User ID"}, {"Last Location.1", "Computer Name.1", "Last Checkin.2", "Status.1", "Computer Model.1", "Serial Number.1", "User ID.1"}),
    #"Sorted Rows" = Table.Sort(#"Expanded Inventory2017-3-14 2-35-10-828",{{"Computer Name", Order.Ascending}}),
    Mergelocation1 = Table.FromRecords(Table.TransformRows(#"Sorted Rows", (r) => Record.TransformFields(r,{"Last Location", each if r[Last Location] is null then r[Last Location.1] else r[Last Location]}))),
    Mergecname1 = Table.FromRecords(Table.TransformRows(Mergelocation1, (r) => Record.TransformFields(r,{"Computer Name", each if r[Computer Name] is null then r[Computer Name.1] else r[Computer Name]}))),
    Mergestatus1 = Table.FromRecords(Table.TransformRows(Mergecname1, (r) => Record.TransformFields(r,{"Status", each if r[Status] is null then r[Status.1] else r[Status]}))),
    Mergemodel1 = Table.FromRecords(Table.TransformRows(Mergestatus1, (r) => Record.TransformFields(r,{"Computer Model", each if r[Computer Model] is null then r[Computer Model.1] else r[Computer Model]}))),
    Mergeserial1 = Table.FromRecords(Table.TransformRows(Mergemodel1, (r) => Record.TransformFields(r,{"Serial Number", each if r[Serial Number] is null then r[Serial Number.1] else r[Serial Number]}))),
    Mergeuser1 = Table.FromRecords(Table.TransformRows(Mergeserial1, (r) => Record.TransformFields(r,{"User ID", each if r[User ID] is null then r[User ID.1] else r[User ID]}))),
    #"Removed Columns1" = Table.RemoveColumns(Mergeuser1,{"Last Location.1", "Computer Name.1", "Status.1","Computer Model.1","Serial Number.1", "User ID.1"}),

Thanks for your help,

Jeff