Application approaching the 6month

I read here that if there is a problem with an application or if it is complex, Home Office will write to explain why it will not be decided within the normal standard. "We will write within the normal processing time for the 8 week standard and within 12 weeks for the 6 month standard."

Does this means that by the 3month I should have gotten a letter to say they will not decide it within the normal standards? Has anyone got such letters and when did they get them?

My application is approaching the 6months mark and I haven't received anything from Home Office.

Do you know if they have access to all previous UK visa applications? I did not provide details of all the previous visas I had and now I am worried that they might be thinking I was an over stayer, I was hoping they would have a record of all my previous visas (Tier 4 student, Tier 1 Post Study, Tier 2 Sponsored, EU Residence Card, EU Settled Status, ILR)

Also I am about to move to a new house. How can I inform them of my new address? Do I need to change the council for the ceremony?