Publisher alternated grades of paper, so the page-blocks look striped; age-tanning is either mild and uniform, or mild to moderate and uniform.

Agent of the Terran Empire (1965) - 3 short stories plus a short novel featuring Captain Dominic Flandry. After 3 Ace-Double halves 1959 to 1961, this and another collection from Chilton (both in 1965) were the first attempt to form a unified and chronological set of the "Flandry" stories. (It just took 15 years for paperbacks of the Chilton collections to come out.) Later books written took place between or before these, which is why there is a "Chronology of Technic Civilization" included in the Ace volumes - which also show that the "Flandry" stories come later in the same timeline as the "Nicholas van Rijn" stories and novels. I recommend this and Flandry of Terra (1965) as good introductions to Flandry.

Tiger by the Tail
Warriors from Nowhere - (original title= "The Ambassadors of Flesh")
Honorable Enemies
HUNTERS OF THE SKY CAVE
(Afterword by Sandra Miesel)

Original appearances from 1951 to 1959 - in Planet Stories (2), Future SF. "Hunters of the Sky Cave" is a re-title of the Ace-Double (half) We Claim These Stars, which in turn was an expansion of "A Handful of Stars" (both appeared in 1959.)

Here's a plot-summary for HUNTERS OF THE SKY CAVE:
[With the galaxy split in conflict between 2 implacable confederations (the Earth-based Imperium and the Mersian Empire), anything ought to go. But how do you plan the ambush and capture of a tremendously capable telepath? The intended victim (Aycharaych) - a weird genius from an uncharted world, and also the right arm of the Merseian general staff - could perceive not only everything thought close by, but was also able to read minds at a distance. So the problem posed to Dominic Flandry, Captain of Terran Intelligence, was a real killer. To make matters worse, the telepath in question was equally interested in putting Flandry out of commission, since the fate of a great number of planets might depend on which of these two won.]