Fortunately, the two Gargos cinematics unlocked properly after a couple of playthroughs in the 3.5 update. However two more seem to be locked, despite supposedly completing the tasks properly:
Lore: The Hatchey’s Secret III
I had posted about my issues with this one previously. I had played the preview and completed this quest line that earned the achievement and also the item. However, once the full SL release came out it was locked. I went through the painstaking Hatchery/stalker transceiver process in full, and it didn’t unlock. I also went through on a separate account (for which I didn’t complete it in preview) in the 3.4 version, completed the quest line, and got the achievement and the item. So, I assumed it was a glitch related to having earned it in the preview release.
In 3.5, I went through the same laborious process again, completed the quest line that previously earned the achievement, and the item was never awarded again, thus still locked. Hopefully the devs can sort this out as I don’t think I can take doing that questline one more time as it seems even rarer for those missions to pop up now.
Status: Titan’s Vengeance (update: Got this by resetting Eyedol’s story progress and playing through again)
This one I’m not totally sure about in terms of requirements, but I completed the Eyedol quests to unlock him, plus I beat Gargos using him 15 times to unlock his mimic skin.
Someone please let me know if I’m mistaken, and this is unlocked by some other means.
Bonus question (if the devs are reading this):
Will there be there any reward for getting 100% in the archives?