Fantastically collectble! All girls' comic titles Holiday and Summer Specials are in high demand, the greatest title being Bunty. But Tammy and Jinty and Tina and Lindy etc are all sought after by collectors. Owing to the fact that they were not kept as much as boy's summer specials were, the girl's ones are much scarcer!
The 1974 issue is called Tammy and Sandie Holiday Special. 1975 one is called Tammy and June Summer Special.
In Dec 2008 on eBay UK a copy of the 1972 Summer Special sold for £37.87.
Note: some PR issues may have no value. Selected issues in FN, VF or VF/NM may not exist in some titles.