I've been looking into the origin of the B/O Electronics brand name and discovered that two of the fakes sold under that name had registered UPC barcodes.
Namely: 618476100560 (Baby Brainy) and 618476010067 (Gigabot).
Baby Brainy barcode
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Gigabot barcode
Those do not seem to exist in any of the barcode databases I tried looking in, but the first digits of a barcode identify the registering company and can be looked up.
https://www.gs1.org/services/verified-by-gs1/results?gtin=618476100560
Note how the last digits of the barcode (without the check digit at the end) correspond to the "ITEM NO" on the boxes.
The barcode is registered to "Pro-TV Development Inc.", more details on which can be looked up from the registrations of their products within the FCC.
The contact person is specified as "NIANZU TANG", which can be another transliteration of "Nien-Chu Tang" seen as the applicant for copyrights over "Furbish" and "Baby Briany" [sic]: https://publicrecords.copyright.gov/detailed-record/19521181.
This company is also known to have produced electronic toys: https://web.archive.org/web/20040103131922/www.toybase.com.tw/tw/t86B49.html.
The domain name "protvinc.com" has expired a few years ago, but the site itself is still up at an alias, protv.com.tw at the time of writing.
On the earlier archived pages, the company is called "Serendipity". https://web.archive.org/web/20010819132337/http://www.protv.com.tw:80/profile.htm https://web.archive.org/web/19981203160530/http://www.toybase.com.tw/tw/t86b49.html
The old site had numerous product categories, including interactive toys, but that part unfortunately has not been archived (look for the "INTERACTIVE TOYS" option in the select menu). https://web.archive.org/web/20010829191021/http://www.protv.com.tw:80/showroom/main.php
Update Jun 4: There is a blog post[1] showing the circuit board of a Furbish, where the label "TF-9901" is visible. On another board shown under Furbish (Furby Fake)/Technical information, that text does not seem to be present, although the component layout matches. This suggests that Teamforce has also been involved.