[p4] Determining original version for newly submitted version?

[Chris Shenton]

One of our developers recently checked in some code and appears to
have blown away a bunch of changes that were previously submitted.  It
looks like he based his changes on version #24 but #25-#28 had been
submitted before he made his submission which became #29. I guess he
said "keep my changes, nuke theirs" to the resolve question :-(

I was trying to reconcile this by finding the version that he started
with (#24) and diffing with his submitted version (#29). But I could
find nothing in the tools which would tell me what version he
*started* with.  I had to do manual diffs between all the versions
until I found something with the fewest changes. 

Is there a way to determine what version a current submitted (or
previously submitted) version was based on, so we can revert and
manually integrate if necessary?

Thanks.