If I had doubts I would say ok you're probably right but like you I have been taught this way and have been doing it like this for many years. I'm not going to say how I know for sure, as I don't want to come across as if I'm accusing your editors and proof readers of being wrong, because they are not, BUT it depends on the context - this is very important. In this context for a poster it would be wrong. For example, you can look at any official letter, more often than not, dates are generally written out in full on 'official' letters (not dd/mm/yyyy) you will see there is no 'of' in the date. In terms of things like writing a date in a paragraph of a body of text the word 'of' when stating a date can somethings apply. For example, in the body of a 'government' letter referring to an incident, stating a time and date in full (with the 'of's etc) is important. There are several other instances where it would and would not apply. Using words like 'of', 'that', 'has', 'have' in the wrong context are known as 'Fillers' that's why 'of' is generally dismissed in dates when 'th' or 'nd' has been used, as it is a filler. Fillers are unnecessary extra words that provide no extra information or meaning to the text in question, therefore has no need to be there at all.
Anyway, enough of that, such a minor detail. Let's go back to the bigger question at hand, which the thread was originally intended - the poster design! :icon_smile: