With help of Gerry and Mins, it became clear that Amdts 86,87 and 88 did not introduce any changes to Volume IV of Annex 10.
Therefore any differences between Annex 10 Vol. IV Amdt 85 and Amdt 89 would be introduced by Amendment 89. From this documentPDF it can be seen that the changes where distributed in state letter 2014/21.
Digging a bit further I found the
minutes of an ICAO Communication Navigation and Surveillance Sub-Group (CNS SG)PDF meeting which included the state letter in Appendix B. You can find it from page 56 to 91.
Amendment 89 contains over 30 pages of changes to Volume IV of Annex 10 and that was more than I had hoped for; needless to say I am not copying all that information into this answer. A summary of changes can be found below.