@daniel any hope for easy fix for us yet sir? , who have already bricked ? I want to stay optimistic 
, should i? 
Redundant bits are stored in the out-of-band area of the flash and used by MediaTek's hardware BCH error detection and correction engine. The feedback provided by that is used by UBI (Linux kernel software layer) to react to correctable bitflips.
I need to make this a standalone topic... 
See my post here, (tldr download and run ./pkg-scan.sh -l, and it should give you what you're looking for): The OpenWrt Firmware Selector - #621 by efahl
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Slightly confused with the new information.
I see the new recovery installer.
mounted ubi0:boot_backup and only had mtd0, mtd1 and mtd2. There was no mtd3 and therefore could not get manufacturing date. Units were purchased in 2021. I really have no intention of ever going back to stock, do I really need to backup?
Some questions before I really screwup.
- After flashing the recovery installer, can I use the latest snapshot now without doing a custom build?
- I see folks using 6.1 kernel, does the latest snapshots contain kernel 6.1? Is kernel 6.1 needed with the new recovery?
Thanks I really need some guidance.
No.
Yes, after force-flashing openwrt-mediatek-mt7622-linksys_e8450-ubi-initramfs-recovery-installer.itb of pre-release installer 1.1.0 you can proceed and flash openwrt-mediatek-mt7622-linksys_e8450-ubi-squashfs-sysupgrade.itb from downloads.openwrt.org.
Yes, the two changes (switch to Kernel 6.1) and switch to all-UBI layout go together -- not because that would have been technically needed, but to make development easier and to avoid (even more) confusion.
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Yes, after force-flashing openwrt-mediatek-mt7622-linksys_e8450-ubi-initramfs-recovery-installer.itb of pre-release installer 1.1.0 you can proceed and flash openwrt-mediatek-mt7622-linksys_e8450-squashfs-sysupgrade.bin from downloads.openwrt.org.
Since this is a pre-release recovery installer, should I wait until it is officially released, or is it critical to upgrade now in order to possibly avoid bricking problems that folks are having. I can wait for a snapshot update.
My two belkins have been running well with snapshots since 2021. Power went out twice last week and both units restarted when the power returned without any problems. I do get nervous when the power goes out since reading about the bricking problem.
Thanks for the previous response, I understand what to do now.
If you've been running snapshots until now and want to keep doing so then you need to run the installer. The fact that I marked the installer as "pre-release" is mostly because of the 23.05.x OpenWrt release being incompatible with that updated installer. So users who want to run the officially released OpenWrt 24.xx will have to wait until it actually gets released, and then I'll also update the installer once again to be based on that official release.
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Updating in the morning. Thanks for the responses.
One of them just died when I flashed the new installer 
... No LEDs over multiple power cycles, no TFTP on ethernet. Don't have time to check serial right now.
Was this one btw:
modelNumber=E8450
cert_region=CA
hw_revision=1
hw_version=48SAR601.0GB
manufacturer_date=2021/07/17
Already updated one RT3200 to 6.1. All is OK. Thanks a lot.
Seems I copied the mtdX files from boot_partition for my devices:
-rwxrwxrwx 1 lynx lynx 512K Nov 13 2021 mtd0
-rwxrwxrwx 1 lynx lynx 1.3M Nov 13 2021 mtd1
-rwxrwxrwx 1 lynx lynx 1.0M Nov 13 2021 mtd2
but how does one extract the serial number, etc?
Isn't this what you're looking for.
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Perhaps, albeit I only have mtd0, mtd1 and mtd2 for each of my devices.
Just look at the contents of mtd5. Clear-text strings.
At least for my RT3200 the serial number (and SSID, wifi password etc.) was in mtd5
(in Linux, maybe "hexdump -C" )
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So to be clear, I overwrote the installer with newer version back in November 2021, but I copied across the mtd0, mtd1, mtd2 files from boot_backup before I did that. Shouldn't one of those files contain this information?
probably. just check the files with a hexeditor or similar.
The serial number etc. are there quite visibly:
This is the start of mtd5 of my manual backup of all mtd sections (made from the initial OpenWrt initramfs session, I think):
sw_version=1.0.0.1
modelNumber=RT3200
cert_region=UK
wan_mac_addr=C4:41:....
lan_mac_addr=C4:41:1....
wifi_2g_mac_addr=C4:41:...
wifi_5g_mac_addr=C4:41:1...
hw_revision=1
hw_version=48SAR601.0GA
manufacturer_date=2020/09/22
serial_number=38E1...
Hmm. I am confused since I only have these three files saved for each, and am really not seeing the info. Sorry I am likely being stupid. But I can't imagine I didn't copy across one of the files from boot_backup back when I copied across the files for each of my x3 RT3200's.
Mode LastWriteTime Length Name
---- ------------- ------ ----
-a---l 13/11/2021 15:15 524288 mtd0
-a---l 13/11/2021 15:15 1310720 mtd1
-a---l 13/11/2021 15:15 1048576 mtd2
I am guessing back when I mounted 'boot_backup', there were just these three files mtd0, mtd1 and mtd2 for each device. Since the backups I have for each just have these three files.
based on your file sizes, those the are mtd partitions after the original UBI conversion.
your mtd / UBI dts / non-UBI dts
mtd0 = bl2 = Preloader (512 kB)
mtd1 = fip = ATF + u-boot + u-boot env (256+512+215)
mtd2 = factory = factory (1024)
but you are likely missing non-ubi mtd5 6 7 : devinfo (128), senv (128), bootseq (128).
(which I have in my manually done backup)
You can compare the 23.05 non-ubi DTS vs. ubi DTS to see the partition definitions.
Does this mean copying the files across from boot_backup wasn't enough to retain this information? Wasn't boot_backup meant to store the mtd partitions prior to the UBI conversion?
Not sure. boot_backup contained at least the "OEM bootchain components", I think, but possibly not all original contents of other partitions.
Daniel's installation script has also varied during the years, so it might have been different in June 2021 (when I got my RT3200 and have taken the binary backup).
Due to flash ECC driver change in mid-2021, many of us oldtimers have had to re-run the installer to rewrite flash "factory", and that run may have destroyed the original boot_backup and created only a backup of OpenWrt bootchain (like Daniel mentions in the docs).