فَإِذَا بَلَغَتْ أَرْبَعَ مِائَةٍ: فَفِيهَا أَرْبَعُ شِيَاهٍ. ثُمَّ فِي كُلِّ مِائَةٍ شَاةٌ.
Translation: Upon reaching four hundred, four animals are due; thereafter one additional animal is due for each further hundred.
At 400 qualifying animals, four become due. Thus 399 entails three and 400 entails four, just as 120/121 and 200/201 belong to different brackets.
From 400 onward, the schedule takes a regular form: each additional complete hundred animals adds one to the due number.