Model F XT "small sticker" dating

[kcrimson]

I recently bought a Model F XT and wanted to know when it was made. I took these pictures:

Spoiler:

https://imgur.com/a/0SidXQe

Something I noticed was that the sticker is very different from what you'd find on most model fs, such as the one featured in this video (at around the 4 minute mark):

While the sticker varies slightly, compared to mine, these Fs generally don't have a sticker on the backpanel, and the sticker on the backplate is much larger and more legible.

I did some searching and could only find three other keyboards like this, two from Ebay (one which wasn't even opened) and one from a Chinese forum.

At https://www.ebay.ca/itm/Vintage-IBM-Mod ... 2614723535:

Spoiler:

https://imgur.com/a/vlE7Sax

At https://www.ebay.ca/itm/VINTAGE-IBM-MOD ... 3218241384:

Spoiler:

This board wasn't disassembled and the only sticker is the backpanel

At http://mouse.zol.com.cn/147/1479514.html (click on an image to see a full album):

Spoiler:

https://imgur.com/a/rkASEJX

Based on these, I've deduced the following:
-"NB" likely refers to "Number Built" and is always 1 higher on the backpanel. It can't be used for an exact date but rather to see if one keyboard is older than the other.
-The "EC" number (192 or 1921581 on my F) on the backpanels appear to be split due to the sticker size; if it is split, then most of these happen to start with "192" and then deviate from the rest (One starts with 477). Otherwise, EC is 192 followed by an ominous 4-digit number. This 4-digit number probably doesn't refer to any date, as one board has "1070" (July 10 1980? Which is more than a year before the IBM 5150 was announced). It also varies greatly across boards despite them all having an NB within 60-200.
-The board that wasn't disassembled appears to have an NB on the backpanel of either 688, 5688, or 4688, depending on how you view it.
-The EC on the backplates aren't a unique identifier as mine is the same as the disassembled Ebay listing's.
-There is a floating 1A/1B number on the backplate, of which my board is the only 1A, which may be part of the number right below it. If it's not part of the number below it, "0271" could mean a date, i.e day (decimal) month (hex) year (last digit), or July 2 1981. This is unlikely as the board from the Chinese forum with a lower NB would then have been made years later, in June 5 1984.
-The NEC Japan 8405X7 could be used to identify my board, as I haven't seen any other Model F XT with that specific chip. Googling "8405X7" brings only two results, both involving a dot matrix graphics chip made in the 90s.
-My foam hasn't degraded (although it is a bit flaky on the edges) and may be made out of Ensolite, which according to a thread at viewtopic.php?t=11657 was used for older boards.
-There are markings on my case, with a '7' written in black chalk, as well as "4.5.84.B". I don't think this is a date because it has the same start of every F XT model number, 4584656.

If you know anything about this or have a board with this kind of sticker, don't hesitate to post something.

[AJM]

That's an interesting subject.
I have mostly UK-made Model Fs, where the stickers are a lot clearer in that respect.
With US-made ones it seems to be very difficult. Even the big stickers - shown in the youtube video - don't show the correct shop date, I think. Most of them show "dates" in the 90s, but some are quite impossible - like this one:

xt78.jpg (143.32 KiB) Viewed 1103 times