Regardless of the decision theory used, your previous calculations can become outdated due to new information. In Bayesian calculations, we normally have the agent update their model of the world based on evidence. In UDT (edited from TDT), the world model remains the same, but the selected agents change. So it isn’t obvious that one is worse than another in this regard.
Oh, so this sounds to me like (I also did a little additional refreshing on TDT), to translate this to philosophy terms I’m more comfortable with, timelessness is about having the agent not identify with its ontology, i.e. it can tell it’s using a map of the territory rather than confusing the two and so can change its map if needed (become a different agent). Although this makes me think maybe that’s not right because it’s not clear to me how you’d come to call the property timelessness unless it has something to do with how CDT relates the world and time.
Oh, I messed up, I mean UDT rather than TDT in the last comment. And in UDT it’s more a set of possible worlds that remains the same, rather than the model of a single world.
Anyway, timeless decision theories are called that because they calculate what a theoretical agent at the start of time would pre-commit to doing in the current situation.