All the references I have state that these stamps were issued on 5 March 1908, although the earliest reference I can find in the philatelic literature is an announcement in the 20 Feb 1909 issue of the Illustriertes Briefmarken Journal.
The basic stamps were printed by the South American Bank Note Company of Buenos Aires, although I suspect the overprinting of the date was done in Paraguay.
All stamps are perforated 11½ and are on unwatermarked paper. Not much is known of the issue and it seems to be rather devoid of varieties. I record a missing numeral “1” of “1908” on the 1c emerald and a pair without horizontal perfs for the 1 Peso light blue.
The only proofs I record are of the 1 Peso, on card, and a printed from a single plate unlike the 1905-10 Peso values which were printed from two plates (frame & vignette.) I record the following colors:
yellow brown carmine dark blue
red olive green dark green magenta
Blocks of all values are known and I record a sheet of the 1 Peso.
Quantities issued have been reported only for the 1c (5,000,000), 5c (1,000,000), and 20c (500,000).
Covers of this issue are not scarce for Paraguay, but I do record some interesting ones:
Single & bisect of 10c lilac brown on patent envelope from VIletta on 27 June 1909 to Shanghai, China via Siberia with Shanghai Local Post markings.
30c + CP 50c & 75c of 1911 on cover to Switzerland with Por Vapor “Asuncion.”
60c + 10c & “1909” 5c on cover to Switzerland per “Vapor Guarany.”