NatMags had overstated the number of full-price issues of Cosmopolitan sold on newsstands. Some 14,340 copies have been reclassified and put into a discounted bracket.
A total of 2,141 copies of Esquire were also misclassified over the same period.
Duncan Edwards, the managing director of NatMags, faced a similar controversy at the beginning of last year, when the Audit Bureau of Circulations had to reissue statements of circulation for nine key NatMags titles. Emap faced similar ABC restatements in 2002.
Simon Kippin, the publisher of Conde Nast's Glamour, said: "This has been happening all too regularly and it is not good for the industry. We all trade on the ABC currency and it is vital that it can be trusted. There becomes suspicion that something is being covered up and it instills mistrust in the industry we work with and serve."
He continued: "A question also hangs over the delay in responding to this kind of mistake. Restatements should happen quickly and publishers should not be able to trade on incorrect figures for six months."
Kippin's sentiments were echoed by a press buyer, who said: "This is an alarming trend. It all comes down to the fact we need more openness to the ABCs. There are so many confusing categories that it makes it easy to hide this kind of thing."
NatMags said in a statement: "Cosmopolitan travel size has been reclassified as 'sold below basic cover price but not less than 50 per cent'. Esquire has had a small number of copies moved from bulk to monitored free."
The ABC declined to comment on the story.
Cosmopolitan is the number-two women's lifestyle title, behind Glamour. It has been talking to Rise Communications and various advertising agencies about a new marketing strategy.