How to create an autonumbering formula based on three columns

Joh_Loh 

Seems I made too much of a meal of this!  As well as generating a code that depends upon the sorted order as opposed to the original order.

This is mainly sorting and formatting

= LET(
    seq,       SEQUENCE(13),
    sorted,    SORT(HSTACK(spec,seq), {1,2,3}),
    autoNum,   SCAN(0, SEQUENCE(13), IncrementAutoNumλ),
    formatted, TEXT(autoNum, "0\,0\,0"),
    SORTBY(formatted, CHOOSECOLS(sorted, 4))
  )

The key is the Lambda function that identifies model changes and increments the code

IncrementAutoNumλ
=    LAMBDA(acc,k,
        IF(k=1,
            111,
            LET(
                changeMake?,  COUNTA(UNIQUE(INDEX(sorted, VSTACK(k, k-1), 1))) - 1,
                changeModel?, COUNTA(UNIQUE(INDEX(sorted, VSTACK(k, k-1), 2))) - 1,
                increment,    IFS(changeMake?, 100, changeModel?, 10, 1, 1),
                acc + increment
            )
        )
    )

Now I guess its time to look at the other solutions to determine how to get the result efficiently!