There is a facsimile drawing of the so-called ‘Bethlehem’ bulla now available. It has been produced by Pnina Arad.
According to the drawing, the first register contains a triangular-shaped ʿayin (ע) and the lower fragment of a taw (ת), yielding the word בשבעת (bšbʿt), meaning ‘in the seventh (year)’. The second register has the leftmost portions of a yodh (י) as the first extant letter. The fourth visible letter has been drawn as a ḥeth (ח), though apparently the vertical stroke in the top left has been broken off. The proposed reading is ביתלחם (bytlḥm), referring to the toponym Bethlehem. The third register has only one extant letter, but on the basis of other fiscal bullae, has been reconstructed as למלך (lmlk), meaning ‘for the king’.
So it looks like the bulla probably does refer to Bethlehem after all. Nevertheless, a personal inspection by another epigrapher (in addition to Shmuel Ahituv) would still be good to double-check.