OA just l presumably always prefixed to the following word. Samaritan occasionally and Mandaic almost always the same. Early Egyptian OfA alternating lh and lˀ but elsewhere almost always with final aleph in the literary tradition and even so in Galilaean and Samaritan where other final long /a/ vowels are regularly rendered with heh.

Note especially that Syriac ܠܐ ܗܘܐ "not" does not have a reference to past time.
Given that in the earliest texts simple "not" is prefixed to its verb, it is probable that the later common spelling with final aleph reflects the interjectional usage with a clear final glottal as often heard in Arabic. One might then distinguish lexically between original lā_ "not" and lāˀ" "no!" in Northwest Semitic.
The Syriac ܠܐ ܗܘܐ is replaced by ܠܘ in later texts, for which see s.v. lˀw, lw adv.