Sometimes it's ideal to collect a not so popular area, country or theme. Stuff usually gets sold at a normal or low price and many items are sold unchecked. That's how I struck lucky when I bought this 1943 set from Curaçao with the Prisoners of War overprint at Scotex the other day.
I bought it as the basic set of four stamps, because I did not have it yet. But when I studied them this morning I found that two of the four stamps had constant varieties on them! The 40c + 50c on 1.40g has a different lettertype for the capitals V and K.
The 50c + 75c on 5g has the constant variety Krljgsgevangenen.
I won't be able to retire on them but they do come at a premium, so lucky me!