I'll tell you what I remember off the top of my head, but I don't think I'll be able to recall the most specific details (someone who has been in the community for longer would be better for that). The earliest mention of a Sintax GBA game I am aware of was a YouTube video in which the uploader said they betrayed the trust of a ROM collector who had leaked prototype builds of some Sintax GBA Digimon games. The one in English was called Digimon Adventure, which is why the defacto name for a lot of these is Digimon Adventure hacks. This game was a port of an earlier game for the SNES. Up until 2020 these leaked ROMs were the only dumps of these games. In 2020 Taizou cracked YJ Encryption, the copy protection of these games. Afterwards, he, yy小龙虾, and RibShark would release ROMs for a large portion of their library, even covering a couple of games that were not just reskins of Digimon Adventure. If anyone found all of the Sintax gba games it is yy小龙虾. The only Sintax GBA games that are dumped to my knowledge can all be found on yy小龙虾's twitter, hhug, and RibShark's twitter, though I am not 100% certain on that, and that does not include the prototype games I mentioned earlier. I do not know what Ge Dou Jian Shian is, but I do know that people have jumped the gun plenty of times on the wiki and added things before they had enough info. Without tone marks or the Hanzi "Ge Dou Jian Shian" does not give great info. The Megaman 5 game is probably just a PocketNES port of the real Megaman 5, though it is worth mentioning that Sintax did release GBC games in GBA shells and did create a game called Rockman X5 (which goes by other names as well). That should at least get you started on your search, Taizou and yy小龙虾 are probably the most knowledgeable people on this subject
Here's the YouTube video
https://www.youtube.com/watch?v=hTgUPOdj9GIEdit: Ge Dou Jian Shen is a way to write Soul Falchion's name. That is a gbc game by Vast Fame, but I think that Sintax borrowed its music in their gba games