The Cosmic Synchro Monsters are upgraded forms of "Stardust Dragon" and "Red Dragon Archfiend". They are not Synchro Summoned in the usual method. The opening theme BELIEVE IN NEXUS originally confirmed the existence of what was later revealed to be the Accel Synchro counterpart/evolution of "Stardust Dragon". Stardust's counterpart ("Shooting Star Dragon") is the only Accel Synchro evolution of a Signer Dragon. Although Jack's new ace monster "Red Dragon Archfiend" ("Red Dragon Archfiend's" counterpart/evolution) is not an Accel Synchro, it uses a method called "Double Tuning" to achieve its evolution and is in the same power range as "Shooting Star". Both monsters were released in Starstrike Blast. Their ATK seems to be their original counterparts' Majestics forms' ATK - 500 (Majestic Star Dragon's ATK: 3800 - 500 = 3300 (Shooting Star Dragon's ATK)) (Majestic Red Dragon's ATK: 4000 - 500 = 3500 (Red Nova Dragon's ATK)). Also their DEF is equal to the ATK of their original forms.
The Limit Over Accel Synchro monster is considered to be the ultimate type of Synchro Monster. In the anime, summoning a Limit Over Accel Synchro requires the duelist to achieve Over Top Clear Mind. Reaching this state will cause the duelist, and their Duel Runner to become a shining gold color, implicating the god-like power involved with performing this type of Synchro Summon.
Limit Over Accel Synchros are Synchro Summoned in a similar way to Cosmic Synchro Monsters. However, they do not require their corresponding Signer counterpart in their summoning requirements. They use 2 normal Synchro Monsters, plus 1 Tuner Synchro Monster, which is the same to how Delta Accel Synchro Monsters are Synchro Summoned.
"Life Stream Dragon" is the only Signer Dragon to have a downgraded form, "Power Tool Dragon", which is a mechanized/shell form of itself. "Power Tool Dragon" searches for Equip Spell Cards and cannot be destroyed when it is equipped with one. This sets up for "Life Stream Dragon" who uses Equip Spells in the Graveyard for protection.
Despite the fact that "Stardust Dragon", "Ancient Fairy Dragon", "Red Dragon Archfiend", "Black Rose Dragon" and "Life Stream Dragon" fought against the Earthbound Immortals in the past, the Crimson Dragon did not awaken the true form of "Life Stream Dragon" in the present when it was going against Devack (a Dark Signer with the very Earthbound Immortal it had defeated 5000 years ago).
It appears that creating new copies of the Signer Dragons cannot be done without imperfections - when Paradox stole Yusei's "Stardust Dragon" by absorbing its spirit into a blank card, the resulting copy was a black-bordered card with a mirrored image, something that was not observed in any of the other cards that Paradox copied. The hologram of the monster, however, was unaltered. In contrast, the card copies of "Red Dragon Archfiend" that Lester created were identical to the real card, but the holograms of the monster itself replaced the red coloration with yellow, purple, and teal, a different one for each copy.
Notably, the male Signers' Dragons are Level 8 while the female Signers' Dragons are Level 7.