Dump Version - Mailing list pgsql-hackers

Hello, dump problems again.
I'm working on a dump ToC parser for spatial database restore
(postgis).

I've noticed that pg_dump-7.3 and pg_dump-7.4 list CAST entries
in different ways. Still 'Dump Version' is the same (1.7-0).

What does 'Dump Version' refer to then ? Are these ToC output
changes encoded somehow ?

TIA

--strk;