January 1973 saw the development of different standards between the US and UK editions of Penthouse. Whilst, the previous year, one cover had been re-edited to be less explicit for the US market (nipples were acceptable in the UK but not in the US) the opposite had started to happen with the pictures inside. Simply put, the UK editors believed that the pictures that started to appear in the US edition in 1973, driven by the ever escalating war with Playboy, were too strong for the UK market and they started to crop or airbrush some of the the photos.
The first victim of this was Australian model and, later, Page 3 girl Maggie Burton. Her UK edition picture shows her posterior artfully cut off to conceal what the US edition showed.
Maggie in the UK version
In the US version she clearly displays her mound between the cheeks of her bottom; the first time this pose had been shown in Penthouse.
This editing of the images would become increasingly common in the UK edition of Penthouse over the next few years. In the UK they had (as had the US) sometimes had to touch up a photo where the model was obviously displaying her labia but as the US edition started to show hints of the models' divided mounds over the next year the UK edition didn't follow. Eventually the UK did stop doing this in the second half of the decade but after this as the US started to show more and more the UK increasingly just left some shots out of pictorials.
Elsewhere, Cavalier, which had always been slower to follow the trends (they were still pubic free as late as 1972, for example) started to jump on the couples bandwagon.