[Koha] Z39.50, ILL, and 952$r

[Mark Alexander]

Our little state (hint: starts with "V") has implemented an
interlibrary loan system that seems to be unable to use Z39.50
correctly to query Koha in order to determine an item's availability.
I'll try to describe the problem and then ask if there's a workaround
in Koha.

The state ILL system, called CLOVER, is able to use Z39.50 to query
our library's Koha installation to determine whether an item is in our
catalog.  We told the state to use the MARC 952$r field returned by
Koha (actually Zebra, if I understand correctly) to determine whether
the item is available.  This field contains the item's due date.  If
it is present and contains a date, the item is NOT available.  If it
is not present, the item IS available.

But apparently, CLOVER is not able to handle a MARC field that is
present sometimes and not at other times.  It requires that the field
be present ALL the time.  That is the explanation given to us by the
state when we asked why CLOVER wasn't working correctly (it keeps
issuing requests for books that it had already requested).  This seems
like a serious bug, because there are at least 80 other Koha
installations in our state.  Unfortunately, CLOVER is closed-source
and proprietary, so there seems to be no way for the state to fix the
problem.

Is there some workaround that I can implement in Koha and/or Zebra to
force the 952$r field to be present in all records returned in
response a Z39.50 query?  I think CLOVER might work if 952$r were
present but blank for items that are available.

Thanks in advance!