How do I tell if my pkg tools are too old?

[Robert Elz <kre%munnari.OZ.AU@localhost>]

Assume I'm a real end user, I install NetBSD by obtaining (downloading,
buying, ... whatever) a CD, and run sysinst to install - just doing
a regulation default install.

Then I go and pkg_add ftp://ftp.netbsd.org/pub/packages/whatever/it/is/XXX.tgz

Or rather - that's what I want to do - at that point, how do I know if
my pkg_add is up to date enough to work properly with the binary package?
And perhaps a secondary question, how do I know I should even ask that 
question?

One answer to this might be "it always is" - that is, nothing is ever done
that allows a binary package to fail to work properly with any older
version of the pkg tools, but I kind of doubt that is the actual answer.
In particular, for example, do very old pkg_delete versions properly
remove everything installed with a new binary package?

Assuming that it is possible that the pkg_tools might be too old to
function properly, how do I find that out?

Two things to note:

1. I didn't ever say how new the NetBSD that was just installed was - the CD
I got might have been given to me by a friend who made and used it 4-5 years
ago (for now let's just assume it is still a supported version so current
binary packages still exist on ftp.netbsd.org).

And 2. no sources (of any kind, including pkgsrc) were ever installed anywhere.

I know how to find out what version is installed (pkg_admin -V), what I don't
know is how to find out if that version is good enough.

If I were using pkgsrc, then there'd be a bunch of (different) tests spread
throughout that that need (at least) specific versions of the pkg_tools,
depending upon what I'm doing (to check the vulnerabilities you need at
least xxx, to check for acceptable licence you need at least ...).   That's
fine, but that's not what is happening.

It seems to me that the only way this could work would be if the
packages themselves say which version of the tools they need (what
assumptions they make about the way the tools work - aside from that
I assume that the only other requirement is that everything be consistent).

Is there something now in binary packages that serves that need?

If not, could it be added?   (and yes, I know that in this case there
is no way to automate the check, as the old tools we want to detect won't
be doing the detecting for us ... but sometime in the future, perhaps
it could all be made to work.)

kre