Rashi: The Torah is simply clarifying its previous statement ¹ - that the accurate assessment that one makes needs to be based on the remaining years until the Yovel.

Seforno: To teach us that one deducts from the total the number of years that the Eved Ivri worked, ² irrespective of the fact that if many years remain until the Yovel, he would have become more experienced and produced better work, and that, if few years remain, the work that he did was not on a par with the work that he would have performed had he remained until the Yovel.

Moshav Zekenim (citing Kidushin 20a & b): The current Pasuk is discussing where the Eved's value increased (he was sold for a hundred Zuz, and his value rose to two hundred), in which case the redemption is based on "Kesef Miknaso" (a hundred Zuz for all the years of his sale); ³ whereas the next Pasuk discusses where his value decreased (from two hundred Zuz to a hundred), and the redemption is then "k'Fi Shanav" - based on his current value (as if he was sold for a hundred Zuz). The Torah is always lenient to minimize the redemption. ⁴

Kidushin, 16a: To teach us that the Eved can acquire himself with anything that one can buy with money - to teach us the principle 'Shaveh Kesef ke'Kesef'' (Things that can buy with money have the same Din as money itself. ¹

Kidushin 20a & b): Refer to 25:51:1:3, and note. We take into account what he was sold for, and deduct for the years that he served - ignoring his current value. ¹

Kidushin, 14b: "mi'Kesef Miknaso" teaches us, on the one hand that an Eved Ivri can be acquired with money, ² and on the other, that he cannot be acquired with produce or vessels that are not worth a P'rutah ³