Some screws are badly over-torqued in my experience and I've often had to exert considerable downwards pressure while simultaneously tuning. All 1xxx screws heads are T5 as far as i know, however I've also seen some screw heads that were quite burred, almost stripped, by previous attempts [not me] requiring replacement afterwards. Maybe it's been got at before, as it's unlikely the screws have been replaced with those of a different head ....?
EDIT: Dasil beat me by ... that ... much [a poofteenth]. So, what he said too. ;)