I've found some topic lately, that compatibility between revisions shouldn't be a problem.
Which topic is that? Not to sound too argumentative here, but in my experience the
opposite is typically true, saved games are usually
not compatible with each other across revisions, and I would be very surprised if a rather old save, even a whole single month old, would work with the current revision.
I can't really speak for the coders, but I don't think a whole lot of work is put into making old saves import/work properly with current revisions - I think that putting coding work into such a thing would really slow down development.
Please keep in mind that SVN versions that are not official releases are not meant to be for continual enjoyment/gaming pleasure, but mostly for bug-stomping and testing new features. This is why not every single revision is worked to be totally bug free - many are in fact quite unstable.
(Edit: Sorry if I'm a little unclear - didn't sleep well last night...
)