במדבר פרק א, מב
בְּנֵי נַפְתָּלִי תּוֹלְדֹתָם לְמִשְׁפְּחֹתָם לְבֵית אֲבֹתָם בְּמִסְפַּר שֵׁמֹת מִבֶּן עֶשְׂרִים שָׁנָה וָמַעְלָה כָּל יֹצֵא צָבָא
For all other tribes, the verse uses the language of לבני with a Lamed in front, but not for the tribe of Naftoli. It is possible to say that until this counting in the desert, the tribes did not encamp within an ordered structure. Rather the tribes pitched their tents in no order but were all mixed together.
Thus, when they now were commanded to count per tribe, it was necessary to announce first that the members of the tribe to be counted needed to separate from all the other population, to the place of the tribe being counted. For example, first to be counted was Reuven. Thus, the announcement went out that all members of the tribe of Reuven should move themselves to a designated area and be counted. And, so the announcement was made 11 times as each tribe was counted.
And the tribe of Naftoli was the last to be counted. Thus, all the other tribes had already “moved” out, and only the members of the tribe of Naftoli were left, and no need existed to make an announcement. Thus, the Lamed indicated the announcement for the other tribes and was not needed by Naftoli.
Why was the tribe of Naftoli counted last? The counting was according to the order of the “flags”, the designated groupings of three tribes, as mentioned in Chapter 2. Naftoli was the last of the fourth set.
Why was the arrangement that Naftoli would be the last of the fourth set (and thus, the last of the tribes)? It is possible due to the fact that the tribe of Naftoli was known to be light on their feet (fast), and the animal allusion from Yaacov was a fleet deer. Thus, their position in the back of the moving nation, allowed that in the event of a need for the nation to stand still or move faster, they could run quickly to all the other tribes, and have the pace of the march changed (to slow down the march if tribes in the back could not keep up the pace; or to go faster if trouble approached from the rear).
במדבר פרק א, מו
וַיִּהְיוּ כָּל-הַפְּקֻדִים שֵׁשׁ-מֵאוֹת אֶלֶף וּשְׁלֹשֶׁת אֲלָפִים וַחֲמֵשׁ מֵאוֹת וַחֲמִשִּׁים:
This is curious that by all the other tribes the number of the population concludes with a complete number in the hundreds, with no tens or single units. The exception is the tribe of Gad (verse 25) which ends in a number of 50 (and thus the total of all the tribes also has a full number plus 50). The same pattern exists in the counting of the tribes in Parshas Pinchas, where all end in complete hundred units, with one exception (Reuven) which has a count ending with 30.
It is well known that in many places the numbers are rounded off (39 to 40, 49 to 50, 69 to 70, etc.). Thus, numbers are rounded off (up or down) to make a number of even hundreds. The only exception would be when the number is exactly 50, and then, the number would not be rounded either way, which is the case in this Parsha.
The difficulty remains for Parshas Pinchas, where the number count is 30, which per the previous explanation should be rounded off to the nearest hundred. Perhaps, one can learn from Parshas Beshalach (Shmos 14, 7) that Paroh sets up his army to pursue the Jews, the verse states ושלשים על כולו (establishing groups of 30). Thus, by an army, a group of 30 is an important number unit. And, thus, in Parshas Pinchas which has a greater connection to a count for military purposes, then a number of exactly thirty would not be rounded to the nearest hundred.
The importance of the number 30 is found in Tanach (Shoftim 10,4, Shmuel I 9,22, Shmuel II 23, 13) and in Gemara (Berachos 32b, Chulin 92a).