> However, descriptive grammarians (who describe language as actually used) point out that this rule does not correctly describe the most common usage of today or the past and in fact arose as an incorrect generalization of a personal preference expressed by a grammarian in 1770.
> Many supermarket checkout line signs, for instance, will read "10 items or less"; others, however, will use fewer in an attempt to conform to what is incorrectly perceived as required by the prescription although this is in fact a clear case of hypercorrection as explained in Pocket Fowler’s Modern English Usage.
> Less has always been used in English with counting nouns. Indeed, the application of the distinction between less and fewer as a rule is a phenomenon originating in the 18th century.
It's still valid using less, though we could pedantically argue senantics.
Lines of code is often used as a term of expense, or expressing a form of cost associated with technical debt. In that context, saying, "500 Lines or Less", is similar to "$50 or less".
https://en.wikipedia.org/wiki/Fewer_vs._less