When "Splitting" isn't enough

I've split my test run and most everything works great. However, how do I
provide a multi-user environment that does not allow each user to view/access
existing records (to prevent accidental data overwritting, etc.), but at the
same time allow the user to "Go Back" to a previous page (form) to make edits
while entering data?

I've performed all the trial-by-error methods that I can think of, in
addition to reading the "Access Bible", but I can't seem to get over this
last major hurdle. Please help before I hurdle myself over something very
high and steep!

Mucho thanks!!!