no they didnt...my 7/74 hq sandman i just sold had no vents and was a brisbane build.
i have seen a 4/74 with vents and if you look at will.co aquamarine van in the hq sandman found thread it has no vents and its 5/74..
also it has nothing to do with the fact that they may or may not be sandmans..all hq vans got the vents deleted around the same time which was just prior to hj production starting.
(the change probably had something to do with the old tooling wearing out and the new tooling for hj being there to use.)this last comment is not fact but is a high probability.