I never stated they were the only people using this date. More research is required to ascertain if this was a date commonly held in various societies as being one of the possible dates of the Noahic Flood.
Well, the drought conditions experienced towards the end of the Egyptian Old Kingdom have been attributed to the cyclical Sahel drying. If you google this, you will find the phenomenon does have a global effect, however it is not caused by catastrophes such as impactors.
As for "evidence of tsunamis and/or floods from all over the world", the world is a very active place, climactically and seismically. There should be no surprise that evidence of climactic and/or seismic events are common. That does not suggest they all happened at the same time due to one global event.
You will notice that I started my list in post 4653 with "4200 years ago..."
Everything I listed is what happened in ca. 2200 BC. So I am saying it all happened at the same time i.e. during the 4.2ka BP event. You can check all of them.
Most scientists are still not certain whether the event happened suddenly or gradually.
The reason why a distinct event has not been picked up yet in ice cores is because to date they have mostly looked at bigger increments such as 50 or 100 years. I believe they now realise that they should reduce their search criteria to 5 or 10 years to pick up a single sudden event. Research is now focussed on this and I am certain we shall see results within the next year or two.