Sakuma Y. 2009b, II, 473 highlights the erroneous form of TAR, missing one horizontal wedge (also the autography in KBo 41). However, some traces are visible before the sign, and it is possible that the wedge was impressed very lightly, so that it is not entirely visible (for the characteristics of the script, see also Introductio).
Tentative. PaceSakuma Y. 2009b, II, 473, there is no space for AR here to accomodate his restoration (UM-MAM[a]r-tu₄-um-[ma-an-na]). See in fact also D. Schwemer in KBo 71, XXII, who suggests this is to be read Tum[manna].