The 55th reunion of the League of Nations took place in Madrid in June 1929. Stamps from the current definitive issues (the Vaquer types, the 1 céntimo printed matter stamp and the yet un-issued recess printed express stamp) were surcharged with a typographic overprint in red and blue "Sociedad | de las Naciones | LV reunión | del Consejo | Madrid." The set was valid only seven days, from June 10th to 16th, 1929, and was sold only in the main post office (correo central) in Madrid and in the branch post office of the Spanish senate (senado) which during the reunion was the official branch for all participants.
The stamps used for this set were not taken out of the regular print run but were printed and numbered apart. That's why most surcharge forgeries of this issue can easily be detected by controling the backside numbers, which run from A 000,001 to A 000,380 (5, 10, 20, 30, 40 and 50 cts); A 000,190 (15 cts); A 000,375 (25 cts); A 000,300 (1 pta); A 000,200 (4 pts) and A 000,150 (10 pts). The highest control of the "pre-issued express stamp" is A 000,180. A second interesting detail is the fact that the surcharged 2 and 25 cts value of this set are always type II and the 15 cts is always type Ia which may be interesting for those who have difficulties to define the differences between types.
Engraver: José Espinós Gisbert (1 ct), Camilo Delhom (express stamp) and Enrique Vaquer | Typographed and recess printing of the F.N.M.T.| Sheets of 200 (1, 2, 15 and 25 cts) and 100 | Perforation: 13:12,75 (comb) | First issued: June 10, 1929 | Valid until: June 16, 1929 | Control numbers on the reverse (except the 1 and 2 cts)