A LIST below compactly presents several such paragraphs and their opening sentences. Its meaning is therefore determined by context. Although Rashi only mentions this principle at the beginning of the paragraph it applies to all VAV in the paragraph. OR, there are 20 years of usage left to the buyer which the original owner has to redeem and pay off. Implicit in here is use of a straight line method.
Many people seek to find some obscure grammatical point.
In other words the interpretation of the verse as referring to the beginning of the Jubilee year is NOT a derivation from the Bible. Rather it is derived from the following Talmudic logic found in Chapter 25 of Rambam, Loans. A general principle of Jewish law is that a contract is always interpreted restrictively. Indeed, the person who owns the contract is using the contract to obtain funds or objects from this fellow man. The general principle then is that the burden of proof is on the person who wants to extract money.