VW used to dip all their cars when being manufactured, my old Golf was also black primered in areas it was impossible to spray in, it was like that because it was dipped.
anyway, if you let the paint stripper sit for a while and use a wire brush to remove paint - it will eat putty, primer and paint, then buff with a wirewheel brush - the little scratches it leaves behind are required for the primer to bond to the metal and then you sand the primer smooth and prep the base ready for spray. I literally hate this process of torching the paint off, you spend money and still end up with a junk paint job.
I had restored my mothers Honda Accord years ago and removed paint like I mentioned, the painter I used was equally doing work with me, I used to spend entire days at the shop working on the paint removal, I did about 60% of the labor myself sanding and finishing the base, and had the denter (panel beater) fix whatever I wanted while on the go.
The result was like factory paint except my finish was glass unlike the orange peel paint Honda painted. It was hard and expensive but worth it, the car looked amazing when it was done. I also plated all bare metal parts and brake lines in the engine bay, and repaired the wiring myself - the tape I used was made by "Tesa" and it was specifically made for engine room wiring.
the payoff was that even after being used in Karachi for a decade, the car still looked good.
