Do universities know if you resat a paper @ AS if you apply with full A level grades?

How do universities even check the grades and the years/how many times you've sat for them? What if you sat for one AS exam first and got a grade you didn't like. And then you reapplied the next year, using a new passport, and sat your AS exam for all four subjects and got good grades and carried those forward for A2 and you got A*s and As.

Do you still have to mention that one exam which was done using an old passport that you resat? Will universities find out about it?

What do I do if I have registered for exams say this summer but never attended them? How do I show them on UCAS or do I have to show them?

Also who should be talking about all these resits or exams that I purposefully didn't attend even though I registered. Like this summer I registered for my AS exams but due to illness and also technical problems the exam boards made about which papers to sit for I couldn't attend the exams. So who talks about these things? The referee or me in my personal statement?