Need advice about merging different versions of a file

[Harry Putnam]

I have need of merging several versions of several files.  And not
sure how to proceed.

The files have been compiled over time on a number of different hosts.

The files contain snippets of information I thought worth saving when
having one or another problem on a number of different hosts.

All the files have a common format.... very basic but common to all
files. 

The files are all kept in hg repos on each host.
The files will contain quite a lot of the same information although
maybe not stated quite the same in all cases.  Also the same kind of
information may appear in different places in each file.

As the files grew, as the number of hosts grew and had different
problems at different times and may have had unique problems on some
hosts etc etc.  Also the hosts have quite a variety of OS's

Any way, over years you can imagine how the files might diverge in all
kinds of ways.

I'd like to merge some of the files but not loose any of the
information.

For example: I have 15 versions of a file named `misc-snp' All are
quite largish somewhere around 16000 lines down to 9000 lines.

In many cases A file may have began life on one host but at some time
was copied to a new host when that host first came online..  and may
have been passed along more than once like that.  So parts of it maybe
identicle but many parts with be different... larger and smaller
amount of data.

The first problematic case I mentioned where the information is only
similar probably cannot be helped and so just not to worry about that.
I'll just have to leave mutiple entries of essentially the same
information just worded differently,

But the second case where the same information may appear in different
spots in the files being compared, and I mean `exactly' the same or
maybe only differing in white space.... what can be done in that case,
far as merging to one file that contains only one spot for that
information?

Can that even be done? I mean in some way not slowly and by hand.