Counting distinct list against multiple contain strings

Hi Peterdown 

Double counting is because you are calculating A, B, and C separately then adding. Instrument matching both 5D(1)(c) and 5D(5A) gets counted once in A and once in B. You can combine with OR in a CALCULATE where each instrument is only counted once

MEASUREA1 =

CALCULATE(

DISTINCTCOUNT('prod extract'[instrument_number]),

LEFT('prod extract'[instrument_type],3) IN {"s46","s48"},

'prod extract'[issued_date_financial_year] IN VALUES(refdata[current_year]),

FILTER(

'prod extract',

 CONTAINSSTRINGEXACT('prod extract'[offence_list],"5D(1)(c)")

        || CONTAINSSTRINGEXACT('prod extract'[offence_list],"5D(5A)")

        || CONTAINSSTRINGEXACT('prod extract'[offence_list],"5D(2)(a)(b)(iv)")

    )

)

For your other measures with up to 7 references, add more || conditions inside FILTER