Is a hyphen optional?

[Tan Elaine]

The Corrupt Practices Investigation Bureau (CPIB) said in a statement on Wednesday that it arrested the then CNB director, Ng Boon Gay, on 19 December last year.
And on 4 January this year, the then SCDF commissioner, Peter Lim Sin Pang, was placed under arrest.

Is a hyphen optional between then and CNB? Sometimes I see a hyphen used after such constructions.

Thanks.

[J&K Tutoring]

In my opinion, the hyphen is not optional- it should not be used. If the director was a "then CNB" director, then a hyphen would be used. Then refers to when he was director, not what kind of director.

[Tan Elaine]

The Corrupt Practices Investigation Bureau (CPIB) said in a statement on Wednesday that it arrested the then CNB director, Ng Boon Gay, on 19 December last year.

And on 4 January this year, the then SCDF commissioner, Peter Lim Sin Pang, was placed under arrest.

Is a hyphen optional between then and CNB, and then and SCDF? Sometimes I see a hyphen used after such constructions.

I cannot quite understand J&K Tutoring's reply. Both Ng and Peter Lim were CNB director and SCDF commissioner respectively before they were asked to step down from their posts as they are being investigated by the police for personal misconduct involving finance.

So I would like to ask again whether a hyphen is needed in each case. Sorry for being unable to understand J & K Tutoring's reply.

Thanks in advance to someone who could clear my doubt.