The reverberations would have no bearing on observing where they were and where JFK or his car when the first “horrible ear-shattering noise” was heard. How would reverberations affect people in the VP car recalling that their car had just completed the turn? or occupants of the VP security car observing that they had made the turn onto Elm and were along side the TSBD?
Another of your so-and-so said arguments and this one isn't even accurate. Ladybird said in here official statement to the WC:
"Then almost at the edge of town, on our way to the Trade Mart where we were going to have the luncheon, we were rounding a curve, going down a hill, and suddenly there was a sharp loud report--a shot. "
Notice she said they "were rounding a curve", not that they "had rounded the curve" which is a significant difference. The Z-film shows the VP car just beginning its turn onto Elm St. when Zapruder resumed filming. If Ladybird is correct, the first shot would have been fired in close proximity to that timeframe. Tom Graves believes it was fired a half-second earlier. I believe it was fired less than one second later. It doesn't matter which of us is correct. Either way it was fired well before your early Z190s estimate which would be over 3 seconds after Zapruder resumed filming.