Kindly add the customary "RESOLVED" to the title of your thread for the benefit of all readers.mac_in_tosh ? TomH TX :
Thank you both for your input. Was finally able to successfully install the update! Followed a tip received from MacInWin (Jake) at MacForums. Booted while holding down the option key and choosing Internal drive from the options list.
I experienced the same thing yesterday after installing the downloadable version. I did a search and there was one site where a poster said there was a new update (17G6030) but there was no other confirmation and on the Apple sites, all I saw was the March 25, 2019 download (17G6029). This morning, the Wikipedia page does list the 17G6030 build with a date of March 29, 2019. So the update after the update that is showing up is probably this 17G6030 build. I did not have a problem with the earlier update on my 2012 MBP. I didn't do the new update after it showed up because I need to apply the update to a couple of computers and would rather wait until the Apple page shows the March 29 date.This update is again showing up as available in the App Store. I thought I just did it ???