Debian/LTS newbie question

["th.pitschel@uni.de" <thp069@googlemail.com>]

Hello list members,

is it correct to assume that in Debian versions entering "obsolete"
state, any "aptitude safe-upgrade" will stop upgrading to newer
packages other than for the reason of security fixes?

When exactly would also the security related upgrades stop?

In other words: what are the exact assertions given by the specific
release states "stable", "oldstable", "obsolete" with regards to
packet upgrades? (when the system is left "as is"; i.e. no adjustment
to the /etc/apt/sources.list)

I searched the general Debian Release info pages, but could not find a
definite answer.

Thanks in advance,
Tom