Welcome to the Forum.
It's possible the business founded by John H Wynn continued to 1967 and items carried the same mark he registered however there are no internet advertisements in the name now. Equally the mark could have been registered by another but it would be unusual that such a maker was also a ring maker.
It's also possible that the date letter has become distorted to appear to be the one for 1967. For the Forum to consider this an image of the hallmarks will be needed.
Alternatively, as the more modern Birmingham maker's marks are not well covered in published works, you may choose to put your enquiry to the Assay Office. If this course is taken would you please let us know the outcome.