In this scenario:
Author A. Has developed his project lasting years (1, 5, 10+ more) Finally gets it Published or Distributed. However, another similar themed work, by another Author; Author B. Gets his work Published or Distributed around the time. Maybe, Days, Weeks, Month or Roughly a Year.
What qualifies, a defense for: "Who Plagiarized Who?"
Well known Examples:
Dennis the Menace (USA March 12th 1951) and Dennis the Menace (UK March 17th 1951)
Heathcliff the orange cat (September 3rd 1973) and Garfield (June 19 1978)
However I have more specific questions, maybe going beyond these two examples.
1 - If Author A. Document with Dates, of early and rough, drafts and scripts, drawings and sketches. Even Copyright, Trademark dates with Publishing company or Distributor. -- What does that mean or effect the case?
2 - Author A. Has an early version; intended to be Published or Distributed, BUT. Reasons were canceled. Years later it finally gets released under another company. But Author B already released their work. -- Does this count has purely coincidentally?
3 - Author A accuses Author B, however the evidence is weak; Both have their own archives but is dismissed by the courts. Reasons being too obvious; just a coincidence, or the Evidence. Inspiration, ARE Unique and Originated from different sources to the Author's lives.
4 - If Author A dies, then Author B releases his Work. But the death of Author A/Family Estate/Production can't make a case, aside from Author A's death. BUT Author B never heard or seen A's work and has proof his own creation has it's own sources?
5 (follow up to 4) Author A's Estates and Production Company attacks Author B's personally and work, by using Media; newspapers or social media. And encourages attacks towards B's associates and company.
Depending how "Badly" it gets; from typical social media behavior to Vandailzation behavior (again depending how badly to goes) can Author B and Production sue for what; based on what damages were caused. Whether Author's A death mattered or contributed; weaponized his death or manipulate to encourage certain attitudes or behavior.