And Aaron; a word omitted in the Samaritan and Syriac, and in the oldest Hebrew manuscript, and marked in the printed copies as dubious. (Kennicott)

Thousand. If we collect the different sums, we shall find other 300; so that the Levites would be 27 more than the first-born of the other tribes, though Moses says (ver. 43-46) that they were fewer by 273. Some say that the 28th verse has been corrupted, (Calmet) or the 22nd, where we read 500 instead of 200. (Haydock)

Others observe, that in the 22,000, the first-born of the Levites and the priests of Aaron’s family are not included, and these might amount to 300 men. (Lyranus)

But Bonfrere rightly observes that this number is too small, as only one is allowed for 74 people. He thinks that the first-born, who were heads of families, are omitted, and those also who were born before the angel destroyed the Egyptians. On this supposition, however, 22,000 will appear too great a number to be produced by the Levites in the space of a year, when some were too young, and others too old, to have children, and others had children already before that event. We may, therefore, either admit the solution of Lyranus, or confess that some fault has crept into the number, though this must be very difficult, since Moses argues in the sequel on the supposition of its certainty. (Calmet)

St. Jerome hence infers, that these numbers are full of mystery; Origen (hom. 4,) says, that the exact number, 22,000, may signify the perfection which God requires from those whom he takes into his service, as there are just 22 Hebrew letters, and 22 patriarchs, from Adam to Jacob, the father of the Israelites. (Worthington)

The 22,000 might be accepted by God, instead of so many Israelites; and the 300 other Levites might be due to him on their own account, being the first-born since the Hebrews left Egypt. (Tirinus) (Du Hamel)