It's canon in the movies/OVA and original first two games (which are based on original novels, as they released before first anime aired). In those, Lina's art is different and she has much larger breasts, despite movie and OVA technically being "prequels" to the TV series. It's an anachronism of Araizumi's. Art provided with novels (like in Dragon Magazine), which was used as the basis for art in first two games (both came out in 1994, first on NEC's PC-98 and then on Super Famicom. They are not same games and differ drastically), also depicts Lina as having quite big breasts. They didn't "finalize" her design by then, yet.