Unfortunately, I cannot see from the photo whether the bottom lacquered bomb has a nose adapter or not, or whether there is a hole to take a nose adapter and it is missing.
In any case, if it does have a nose adapter/hole it is not marked to any marking system of the time. If it does not have an adapter hole it is nothing to do with 3" mortar practice, unless it is something to do with Stokes, about which I know very little. All 3" Practice bombs had a nose adapter, right up to the Mk 8,which lasted until overtaken by the 81mm Mortar system.
The other bomb is marked correctly for both the Pre '44 and '44 - '48 marking systems. The yellow band indicating 'Practice' for the Mk III bomb of the pre 1944 period. The MkIII bomb was produced using the empty bodies of the HE and Smoke bombs to meet the vastly expanded wartime production targets for live types of bomb, hence the buff coloured body below the bourellet.
Had this been a Mark I or II bomb it would also have had a red filling ring indicating the presence of the GP burster under the adapter ring.
Marks I and II were used with Fuze 150 or 150P and later with Fuze 152 or 152A. By the time of the Mk III no live fuze was fitted and the Plug Representing Fuze 162 was used, therefore no red filling ring was required.