St. Vincent - Shells Issued Multiple Times ?!

Hi,

St. Vincent issued a definitive stamp set for shells in 1974 (18 different stamps). Some of the stamps have been issued again in 1976 AND 1977, some only in 1976 again, others only in 1977 again.

The simplest reason is that for some of the stamps and their face value the Post ran out of stock and therefore issued additional copies (while the stamp image looks exactly the same they differ in:

1. 1974: No year imprinted
2. 1976: Year 1976 + (printing house ?) imprinted
3. 1977: Year 1977 + (printing house ?) imprinted

Can someone confirm that in fact stock shortage was the reaosn that some of the stamps have been issued twice or three times ?

It appears likely that there was demand for the standard rate stamps used on personal mail during that time period. Can't confirm it but several printings to replenish a commonly used rate would appear to be a reasonable explanation.