If a company, with which my company has long been in cooperation, is celebrating its 20th birthday, what is the correct way of expressing my well wishes for them on the occasion of that anniversary?
- Best wishes of constant success and progress for 20 years anniversary!
or
- Best wishes of constant success and progress for 20-year anniversary!
or
- Best wishes of constant success and progress on the 20-year anniversary!
or
- Best wishes of constant success and progress on the 20-years anniversary!
or
- ?
Will any of these not sound as if I were wishing success and progress for only that one day?
Should it be "20-years anniversary" or "20-year anniversary"?