Then you are very lucky.
There are no visas that allow employment. A work permit is what enables you to work.
My O visa has "employment prohibited" written on it. My work permit overides that prohibition.
Retirement extensions should prohibit employment. I would imagine that something has been done at the Labour office or they have missed it. You are the only person I know of, out of about 11, that has not had to change. Maybe they will ask next year.If you do have to change reason for extension then it is easy to do.
They are trying to close the loopholes at the national level. With the new regulations about all teachers needing a degree; something which Immigration are now enforcing, they are trying to stop people working on "Os" full stop. Some labour offices will not issue a work permit on a marriage extension.
There was a time when the work permit and extension were tied together, and the expiry dates would be the same. The process now is that you apply for and receive the work permit first. The work permit will be issued upto end of contract date. You can, therefore, work on a multi entry O and only have to apply for a work permit once a year. Under the old system the extension was done first and the work permit would be issued up to that date, meaning that those on a multi entry would have to apply for a work permit every 90 days.