If we think in terms of fortnight periods, then we need 26 such to reach as near as possible to a year. 26 * 14 = 364.

I guess that we should disregard the three rows in the beginning (nos. 1-3) because they seem special, e.g. they have parallels in other tablets and may therefore be a description of new year festivities or something like that. 31 - 3 = 28.

And in a similar manner I would like to discard row no. 31 as a special period. 28 - 1 = 27.

Assuming these things, we will find that row no. 30 must contain the missing night, the night which is needed in order to reach 365. The number of the rows nos. 4-29 is 26.