The Headgasket must be matched up perfectly with the OEM one, VW produces several different headgasket for the same engine.
Was the headgasket purchased from a VW dealer?
Yeah it does only go on in one direction, but VW produces more than one headgasket for the 1.8T engine.
Im not saying this is your issue, but if your not getting any oil into the cylinder head its something to think about.
Have you removed the valve cover at all to see if there is fresh oil up there?
Removing the oil cap wont produce any real results because there is an oil baffle you are looking at when removing the cap. the oil it designed to stay underneath this baffle so the top will look dry.
Does the engine have loud tapping noises?
Are there any shops local to you that advertise a bilstien engine flush or something similar?
VW dealers have a engine flush kit produced by BG products that is meant for oil sludged 1.8T passats, but i have done this service on other VW's with the same filter housing (yours will apply). You may want to try and flush out the oil galleries to see if there is any possible blockage.
Yes you are correct, however there are very small differences in the headgaskets, VW produces several versions of the same headgasket with little differences (for example the 1.8T has almost a dozen different cylinder heads which are basically the same just with small differences).
Have you performed an oil pressure test? Test the pressure at idle and at 2,000rpms or when the low oil pressure light comes on.