Unless it works differently for pipes destined to go abroad your set could be a few years older than the seller indicated.
You would expect to see a Royal Warrant - the Prince of Wales feathers - above the text inside the fitted case of a set from
1928 as for example on this case from
1922 ...
View attachment 89468
... and on this case from
1930
View attachment 89470
Moreover, the fitted case would not be pre-1921 carrying 1928 pipes as I believe the custom was to make the cases to fit the pipes and not the other way round.
According to John Loring, "In 1921 the Royal Warrant was received by Edward, Prince of Wales and his Royal Crest was used up to 1936 ..."
View attachment 89471
An example from
1920 of case nomenclature which looks identical to the nomenclature on your case
View attachment 89469
View attachment 89472
