Another general question about my 1990 190E 2.0

Yesterday I took a look at the ignition timing. The car appears to be fitted with a TSZ type ignition and not the EZL type as everything seems to match the pictures in my Haynes manual, and there's no sign of a EZL resistor pack.

When putting the strobe timing , I see the ignition is right about TDC, or perhaps a few degrees before. The manual tells me I can change the timing the traditional way, by rotating the distributor, but when I try this the engine speed changes (as expected) but the strobe still gives me EXACTLY the same reading.

I did some searching before posting this and came across a couple of posts from a guy with a similar looking problem. One of the posts did mention that the timing simply wasn't modifiable.

My questions are:

1) Do I have a TSZ type ignition?
2) Is the timing reading of around 0 degrees TDC OK?
3) If it's not OK, how can I change it?

Many thanks

Mark