Sequence 3 and 4 have a a total of 14 memories.
This achievement is specific to only sequence 4, but I have included sequence 3 in the list because there is no specific achievement for only sequence 3.
I wrote this guide as a simple checklist (click on the spoiler if you do not mind seeing the title or “subtitle” of the memory) to help you keep up with: what you have completed, how many memories you have left in the sequence, which memories have secondary objectives, and what those objectives are (so you can prepare before starting the next memory).
*** Spoiler - click to reveal ***
Sequence 3
Memory 1: At the Pub, “Interrogate the drunk Captain to find out what he knows”
Memory 2: Prelude to Rebellion, “Stand up for the people”
2ndary Objective: Use your fists to knock out opponents
Memory 3: Elegant and Deadly, “Protect the family business”
Memory 4: Vanishing Slaves, “Prevent the strange cargo from reaching its destination”
2ndary Objective: Race through the checkpoints faster than your opponent
Memory 5: Storming the Fort, “Chase the ‘villian’ to the fort”
Memory 6: In Vinos Veritas, “Follow the instructions and disrupt order”
2ndary Objective: Don’t increase your notoriety
2ndary Objective: Carriage must retain at least 50% health
2ndary Objective: Kill all targets in 1 minute
Memory 7: Getting Uloa’s Attention, “Send the governor an explosive message”
Memory 8: A Governor No More, “Draw Governor Uloa out of La Balize”
2ndary Objective: Set up the ambush in under 4 minutes
Sequence 4
Memory 1: Southbound, “Find out where the slaves are going”
2ndary Objective: Do not swim
Memory 2: A New Life, “Be welcomed into a prosperous and free community”
Memory 3: Gathering Tools, “Fashion a weapon out of the materials at hand”
2ndary Objective: Don’t enter open conflict
Memory 4: The Company Man, “Discover the colony’s dark secret”
2ndary Objective: The captive man must retain at least 50% health
Memory 5: Trail of Truth, “Follow the clues to unlock the past”
2ndary Objective: Do not engage in open conflict
2ndary Objective: Complete the mission in 5 minutes
Memory 6: The Secret of the Cenote, “Search for the lost Prophecy Disk”
2ndary Objective: Take no damage
2ndary Objective: Solve the puzzle in 2 minutes
To keep this solution clean and concise, I have not included hints for the secondary objectives. I wrote this to help in planning ahead (getting enough poison darts, bullets, or smoke bombs) to make the second objectives easier. Please comment if you do need any help and I will provide any help or suggestions I can. I hope you find this helpful and good luck going for 100% sync!