(1) Discontinuance against any defendant takes effect on the date when the notice of discontinuance is served on that defendant under rule 37. 3(1) (a).
(2) A claim or the relevant part of a claim is brought to an end as against that defendant on that date.
(3) However, this does not affect —
(a) any proceedings relating to costs; or
(b) the right of the defendant under rule 37.4 to apply to have the notice of discontinuance set aside.