I'm gonna create a hypothetical scenario here:
John is a character on Mizahar. He is in Fall 511 in Syliras, but he makes a Flashback thread in Sunbert. The thread is Timestamped Summer 509, and in this flashback thread he acquires a new and fancy sword. Would John be allowed to use this sword in a new thread in Fall 511?
If you didn't understand that, I can try to rephrase: Will I be able to use an item I acquired in a flashback thread in a up-to-date thread?