semi-brick EMMC problem?

I have an early HD+ that had been updated to an Android 4.2 and then 4.4 using AndroidForNook's AFN semi-commercial SD cards.

It was slowing down and crashing more - I guess with Google's Chrome and other 'almost system' updates.

I decided to go for a CyanogenMod distro - many weeks ago now. I don't remember exactly which - not the most recent, Android 4.4 type, probably 10.xx. I made an SD card - I am a very competent Windows admin and CMD user. Know next to nothing of Unix/Linux/Android systems. Used the same SD card that worked with AFN. Consequently Nook would get as far as showing B&N Nook splash screen w/o SD card inserted; or AFN's menu that would respond to volume and N buttons, but stick at "loading ....." whatever I'd chosen with the ORIGINAL AFN image on the inserted SD.

Followed a couple of weeks of trying several 'recovery' images that mostly did not get as far as screen output. Apparent resolutions focused on SD card boot issues - which I followed at length, ordered new SD cards etc.

TWO things still produce results: a no-EMMC SD recovery that boots to TWRP - but that seemed to work only ONCE; and when part booted with the ORIGINAL AFN SD I can get a shell session as root via ADB. Below are some of my findings...

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File system commands like mount, parted, dd hang when dealing with /dev/block/mmcblk0

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Relevant parts from the kernel boot-up log???

<6>[ 2.412078] mmc0: new high speed DDR MMC card at address 0001
<6>[ 2.412567] mmcblk0: mmc0:0001 MAG2GA 14.5 GiB
<6>[ 2.412872] mmcblk0boot0: mmc0:0001 MAG2GA partition 1 2.00 MiB
<6>[ 2.413116] mmcblk0boot1: mmc0:0001 MAG2GA partition 2 2.00 MiB
<4>[ 2.415679] Alternate GPT is invalid, using primary GPT.
<6>[ 2.415863] mmcblk0: p1 p2 p3 p4 p5 p6 p7 p8 p9 p10
<6>[ 2.418334] mmcblk0boot1: unknown partition table
<6>[ 2.419281] mmcblk0boot0: unknown partition table
<4>[ 2.666687] mmc1: host does not support reading read-only switch. assuming write-enable.
<6>[ 2.685424] mmc1: new high speed SDHC card at address aaaa
<6>[ 2.686248] mmcblk1: mmc1:aaaa SU08G 7.40 GiB
<6>[ 2.705169] mmcblk1: p1 p2 p3
<4>[ 2.924194] mmc2: card claims to support voltages below the defined range. These will be ignored.
<4>[ 2.943786] mmc2: queuing unknown CIS tuple 0x91 (3 bytes)
<6>[ 2.944488] mmc2: new SDIO card at address 0001

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Can not mount SDCARD in the current half-booted state. looks like fstab is not read at startup; however /etc/recovery.fstab exists and is readable.

~ # mount sdcard
mount sdcard
mount: can't read '/etc/fstab': No such file or directory

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Don't really understand what below implies - can read an ACTUAL GPT partition table off an ACUTAL storage device?

cat /proc/partitions
major minor #blocks name

179 0 15267840 mmcblk0
179 1 128 mmcblk0p1
179 2 256 mmcblk0p2
179 3 15360 mmcblk0p3
179 4 16384 mmcblk0p4
179 5 49152 mmcblk0p5
179 6 49152 mmcblk0p6
179 7 458752 mmcblk0p7
259 0 688128 mmcblk0p8
259 1 475136 mmcblk0p9
259 2 13500416 mmcblk0p10
179 16 2048 mmcblk0boot1
179 8 2048 mmcblk0boot0
179 24 7761920 mmcblk1
179 25 306176 mmcblk1p1
179 26 613376 mmcblk1p2
179 27 6831104 mmcblk1p3

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SO - does the above imply a SERIOUS problem with the emmc MAG2GA memory device (thanks to a bug in some distro...); or do I need a proper rebuild of the GPT partitions that will finally allow the Nook to boot properly from a recovery SD and accept an original B&N 2.1 image?? I do have my serial number and don't mind a bogus MAC address in the /ROM directory.

Many thanks in advance. Chris