Why has DWP put a "special marker" on me that affects any benefit I claim?

What does this mean?  Just told by the Centre for Health & Disability Assessments that there is a "special marker" on my file which means it doesn't matter if I return my UC50 on time or even if I return it at all.  I've been told this before over the years, including back when I was on ESA.

Basically my UC50 was sent to them a few days ago.  The deadline to receive it is in a few days and I called them to make sure they got it.  We used tracking and tracking shows it arrived at their "post handling" place last Friday. 

 The person I spoke to looked up my details on her screen.  She then said that the form takes a couple of days to go from post handling to their medical team BUT she says “in your case it doesn’t matter.  There is no deadline.”

I repeatedly asked her what she meant and she insisted there is a special marker on my case saying that it doesn’t matter when or if I send back the form, they will still proceed. 

What does that mean?  I came across this in the past with my last PIP claim (actual claim not just a review) where I never even sent in any PIP form whatsoever or sent in any medical evidence at all but they still proceeded with my claim and I got a PIP Award.

I also notice they almost always do paper-based assessments on me. 

What is this special marker????