This is the twenty-ninth instalment of the Fortnightly Topic Challenge described here, with topics suggested and voted on here. This fortnight's topic is retrograde-analysis (suggested by user24580), and will span from the the 21st of March to the 4th of April. During this period, we will compile the list of questions with this tag and post it as an answer to this question.
In the meantime, please go and propose and vote on future challenges!
Everyone have fun, and happy puzzling!
Link to other Fortnightly Topic Challenges.