syseng68k, now I understand - my thanks for the explanation on timestamping - it makes sense to me now...the "ACARS" item turned up because of previous discussions on timestamping of messages and I had incorrectly assumed your reference.
MurphyWasRight, thanks - much clearer; - that's what my rudimentary "strobe" example was trying to convey. I know about flight data analysis but much less about data transmission protocols so I appreciate all explanations.
I considered the notion of "lag", (which it isn't, really...), to be important for the very reasons cited and in response to Machinbird's concern about "elevator split"...that what is in the minutae of the data may not re-present exactly what occurred - I've seen such disparities lots of times and the context (did other systems, or the aircraft, exhibit behaviour commensurate with the split?), often supports the notion that (for example) the flight controls weren't out of sync. It is offered as a caution to be mindful of the process of recording and interpreting...that reading recorders is not at all straightforward.