1940 The 1st Anniversary of Chaco Boundary Peace Conference, Buenos Aires

Stamp 522
IK-s.jpg 50C
orange
Stamp 523
IL-s.jpg 1P
purple
Stamp 524
IM-s.jpg 3P
multicoloured
Stamp 525
IN-s.jpg 5P
carmine brown
Stamp 526
IO-s.jpg 10P
rose violet
Stamp 527
IP-s.jpg 20P
violet
Stamp 528
IQ-s.jpg 50P
green
Stamp 529
IR-s.jpg 100P
black

1940 The 50th Anniversary of Pan-American Union

Stamp 530
IS-s.jpg 50C
reddish orange
Stamp 531
IS1-s.jpg 1P
green
Stamp 532
IS2-s.jpg 5P
dark blue
Stamp 533
IS3-s.jpg 10P
brown

1940 Airmail - The 50th Anniversary of Pan-American Union

Stamp 534
IT-s.jpg 20P
carmine
Stamp 535
IT1-s.jpg 70P
blue
Stamp 536
IT2-s.jpg 100P
green
Stamp 537
IT3-s.jpg 500P
violet

1940 The 100th Anniversary of First Adhesive Postage Stamps

Stamp 538
IU-s.jpg 1P
multicoloured
Stamp 539
IV-s.jpg 5P
multicoloured/green
Stamp 540
IW-s.jpg 6P
reddish brown/ultramarine
Stamp 541
IX-s.jpg 10P
red/black

1940 The 100th Anniversary of the Death of Dr. Rodriguez de Francia, 1766-1840

Stamp 542
IY-s.jpg 50C
carmine rose
Stamp 543
IZ-s.jpg 50C
violet
Stamp 544
IY1-s.jpg 1P
multicoloured
Stamp 545
IZ1-s.jpg 5P
blue

1940 National Mourning for President Estigarribia

Stamp 546
JA-s.jpg 5/50P/C
black/orange