my 17ssv redline came with 20inch factory fitted wheels and has full size same design / colour black rim/tyre in the front sized wheel
There's all sorts of things that could have happened ...
You could get the factory fitted wheels & of course they arrived at the dealer with the wheels fitted - and also the matching spare.
You could get the same wheels fitted by the dealer, and if you paid full price it was more expensive & by default didn't have the matching spare.
You could get a set of 5 wheels fitted by the dealer, more expensive again.
You could negotiate with the dealer to get it to cost the same dealer-fit as factory-fit (dunno why - maybe to get a car in stock?); and you may or may not know about the spare situation so may or may not get it included.
You might have ordered the factory wheels & the dealer found a car already fitted with 4 wheels on another lot; and organised to have it sent over, and forgot about the spare.
You might have ordered the factory wheels & the dealer (or manufacturer) somehow stuffed-up the order, and when it arrived the dealer went "oops" and fitted the 4 wheels or the 5 wheels depending on how much they were paying attention.