They are cumulative so you only need to apply the lastest patch. ESXi contains two firmware banks. When you install ESXi the partition Hypervisor1 contains the release install and Hypervisor2 is pretty much empty. When ESXi boots Hyperviser1 is mounted as /bootbank and Hypervisor2 is /altbootbank. When you patch ESXi the new firmware is written to /altbootbank and when ESXi is rebooted, Hypervisor2 becomes /bootbank. If there's a problem with a patch you can press Shift+R during the initial boot screen to revert to the prior viersion of ESXi that you had installed.
Excellent, thank you Dave.
I didn't know about the Shift+R, so thank you for that as well and the info about the partitions.
Also, I observed, because of the flaky nature of my boots, from a USB stick, is that if the next boot, after applying the patches does not complete normally, then the following boot reverts back to the original boot bank, so the prior version is loaded automatically.
I'm not sure, if at this point the Shift+R would force it to use the new bootbank, as I didn't know about that either. I just re-applied the patch, and rebooted, with fingers crossed.
The download size for patch ESXi500-201111001 is smaller than the previous patch ESXi500-201109001. Seems a bit suspicious. Also, the bulletin list column doesn't seem to reference the prior fixes for each new patch. The download page surprisingly doesn't address this at all.