I cant speak for rallycars but on racecars its not unusual to have 4 retaining plates holding the screen in 2 at the top and 2 at the bottom , in fact a bonded in glass screen is a real pain in the ass with a seam welded car with good structural rigidity - they crack very easily when you jack the car up on 1 side only !!
To get round this Isoclima developed heated Perspex /polycarb screens that you could change in seconds , they were of course £2000 tho !