Unfortunately, I have a fairly strong suspicion that the letter codes in this series of cartridges were all based on the
game's title (in Chinese), and not anything relating to the developer or publisher. (Links given below are to SegaRetro wiki pages with box scans.)
The Chinese title for A Bug's Life is 蟲蟲特工隊,
Chong
Chong Te Gong Dui.
The two Mortal Kombat-titled pirates -
Top Fighter 2000 MK VIII and
Mortal Kombat 5 Sub-Zero - have codes starting in ZR, for 真人快打 (
Zhen
Ren Kuai Da), Mortal Kombat's Chinese title.
Pocket Monster is BK001. The Chinese title given on it is 比卡超 (
Bi
Ka Chao) = "Pikachu".
This series of games definitely has connections to Gamtec and/or its related companies (Chuanpu, NeverEnding), but I'm not sure which of this tangled web of companies was specifically responsible.
Edited to add: A couple more examples demonstrating the pattern, via SegagagaDomain:
The Lion King 2 = SZ006 = 獅子王 (
Shi
Zi Wang)
Super Donkey Kong 4 = DJ004 = 大金刚 (
Da
Jin Gang). This one's a bit odd, because it doesn't use the same yellow oval for the product code as the other games do, but the numbering scheme is still very much the same.
As for the Gamtec connections:
* The "MD compatible" logo seen on some of these games is exactly the same one found on several games that are known to have been developed by Gamtec-affiliated companies (e.g., the GM-95 series,
as documented here by taizou). It doesn't seem to have ever appeared on any other unlicensed developer's work.
* A Bug's Life uses the High Seas Havoc sound engine, also used in numerous games developed by the Gamtec-affiliated Chuanpu and NeverEnding Soft teams.