The 4.5" Howitzer was still in front line service at the beginning of WW2, examples being used with the B.E.F. in the middle east and in Home Defence.
My home town in 1941 was defended by three troops of 4.5 Howitzers (12 guns), four coast defence batteries (6 inch and 12 pdrs), 4 HAA batteries, various LAA postions, Pillboxes, Depth charge road craters, flamefougasses, AT blocks and ditches and a Brigade of infantry.
Post WW1 dated cases are rare, I'd imagine that there was still a huge number of cases manufactured during 1814-18 that post war production was very small?
Quatermass