DOS/VS keeps a RLD (relocat dict)-items since a very long time. It was
there when I touched DOS/VS the first time in 73.
In fact when I worked for a service bureau with 15 datacenters (from
1975), we had just one installation that had no relocatable loader
(i.o.w. a more current version of DOS/VS)
All, but very few programs will automatically be subject for the
relocatable loader. B and A-transient comes to mind (is that still so?).
What VSE still not does is to keep an extensive ESD (external symbol
dict). Without that it is simply impossible to replace a single CSECT in
an existing PHASE.
It is still possible to take a PHASE (zOS speak a "load module") and
transport the TXT cards and the RLD-cards and that in z/OS.
Don't know if there is a way the other way around (starting from
producing TXT and RLD cards in the required antediluvian format).
Martin