The ITRF2005 is the first rigorous combination ensuring ITRF and EOP consistency, based on time series of station positions and Earth Orientation Parameters (EOPs). The objective of the presentation is the development of a combination strategy allowing to ensure the ITRF2005 and IERS 05 C04 consistency with time. Combining additional input time series after the release of ITRF2005 from the four techniques (VLBI, SLR, GPS and DORIS) allows the assessment of two main procedures: (1) using CATREF combination model and (2) using EOP-only combination method. The main features of the two combination strategies are presented together with numerical application. Comparisons of results obtained by the two procedures will be discussed in an attempt to evaluate the current accuracy of EOP determination by space geodesy techniques and to guide our conclusion for future development.