Also no expert, but agree with GeoffHa.
As for the question, why does Maury say that Imperf examples are known, though without price for used: I find the following in my copy of Yvert Specialisé, v 1:

Translation of the most relevant lines: "After 20 July 1871, the only difference between French colonial stamps and those used in France itself was that the former were imperforate. … Stamps for the colonies were taken from French stocks before perforation or, if there were no extra imperforates of the right denomination to hand, they were specially issued as such."
Therefore, I presume that some of these imperforates destined for the colonies remained behind in France but couldn't be used for domestic postage.