if you let a thought truly slide away in meditation, it’ll be well and truly gone. to make sure you remember it you sort of have to keep a little reference to it open for X time before it’ll take hold in recent memory.
This is a problem for wanting to note down a thought while meditating. Either you do actually write it down as it happens, or you truly let the thought pass by, in which case you’ll just have to hope you’re lucky that it returns later. There is no in-between of “I won’t hold this thought, but I’ll remember it and write it down when the timer goes off” - that is holding on to it (sort of “in RAM”).