It's not possible to flash all updates safely. The TV does *NO check*.Essentially, what you need to do is flash a Full Firmware to avoid a brick.
Full firmwares (we could also call them milestones) are epks that ship all the partitions bundled in.
On the other hand, Partial Firmwares only ship SOME of the partitions.
The problem is that while new partial updates are designed to work on older partitions, new partitions don't expect an older version of other partitions to be flashed, and may act weirdly, crash, or just do nothing at all.
How to know if the firmware you're going to flash is good? The only true way would be to extract the EPK and check it out...but there's a trick
You can perform the following steps to get an EPK that should be good to go and safe:
-> Dump the TV NSU Request
-> Modify the reported firmware version to be something older than you currently have. You may set it to be older than the first released version (in some cases you can get the first version ever released by doing that, or the first milestone). Or you can incrementally reduce the version until you pick an update. My recommendation would be start from a low MINOR, but with the same MAJOR, so that you don't get another partial update.
-> Send this modified NSU Request to LG (i have a tool that i may polish up and release for this task)
-> Copy the CDN Url, download the epk on your PC, and spoof/serve it with NSU_EMU
ALSO check the size of the epk file. A small epk file is unlikely to be a full upgrade.
Now unfortunately, about your brick, there's not much you can do. Your only hope to get it fixed is to try and get serial working, but at your current situation you would need to disassemble the TV, and i'm not completely sure about the recovery procedure in case you get a working connection. I DO have a theory, but i never worked with a bricked WebOS device and someone willing to take a closer look..yet
Hope this post can be helpful to others.
@SIMON: You should add this as a warning
P.S. About the NSU_EMU rewrite i had in progress...i'm lacking time lately, and my main PC has been out of service for a while. I need to get some time and reorganize my storage space before i can get going again.