  Three topics related to computation of the combined IVS EOP series are
discussed. The first one is the consistency of the VLBI EOP series with the
IERS reference frames ITRF and ICRF. Not all IVS analysis centers use ITRF/ICRF
as reference system for EOP solutions. Some of them realize global solution for
simultaneous determination of CRF, TRF and EOP with no-net-rotation constrains
w.r.t. ITRF/ICRF. Analysis shows that such a method can hardly provide
consistency of computed EOP series with the IERS reference frames with
sufficient accuracy. Direct use of ITRF and ICRF for computation of EOP series
submitted to the IERS seems preferable. Second problem is the long-time
stability of the IVS EOP series. Analysis of yearly biases w.r.t. C04 and NEOS
is presented. A possible ways are proposed to save long time stability of the
combined IVS EOP series. At last, various strategies of computation of weighted
mean value are considered. It's shown that usual methods used for this purpose
do not provide satisfactory result for the error of the mean. A new method is
proposed.
