Help me to find the year of these stamps

[pepino]

Hello,
I had about 20-30 Viet nam stamps with no year written on them and I found what year are the most in my catlog. But I didn't found the year of these 3 stamps. Please tell me what are the years of these 3 stamps.
Image: http://imageshack.us/photo/my-images/573/img4307q.jpg/
Thanks in advance
Regards from Bulgaria

[-peripheria-]

Hello,

Here is informations which you want to know.

No 1: VN catalogue: 10 (Republic of South Vietnam). 80th Birth anniv. of President Ho Chi Minh. issue: 19 May 1970.
(President Ho Chi Minh watering star-apple tree) Designer: Trần Huy Khánh
http://vietstamp.net/Product/1334/

No 2: VN catalogue: 226. The war effort. issue: Dec. 15th 1968
(US aircraft downed, after the caricature by Mai Van Hien)
http://vietstamp.net/Product/1815/

No 3: VN catalogue: 13 (Republic of South Vietnam). 2nd Anniv. of founding the Provisional Revolutionary Government of the Republic of South Vietnam. issue: 06 June 1971. Designer: Hồ Thọ
http://vietstamp.net/Product/1337/

Best regards from VSC.

[pepino]

Thank you very much my friend