Recycled Chatto covers: Nightmare Suspense Library #'s 8 and 9

In a recent post on consecutive issues of Yaffa's Mystery Suspense Library I mentioned that it was irregular to find a recycled cover for fresh interior content. In that instance, the new story beneath the recycled Chatto cover was Black, the Blood Of Evil. This story had in fact been published before by Yaffa in Nightmare Suspense Library #8:

This is an issue I'd previously referenced briefly, unaware at the time that the cover was recycled for the next issue in the series, Nightmare Suspense Library #9:

As per the recycling in the Mystery Suspense Library issues, the content of this issue is different to Nightmare Suspense Library #8 - the story is titled The Edge of Fear.

Now, not only had The Edge of Fear previously appeared in Yaffa's Horror Suspense Library #1 and #3, both under Chatto covers, but it was subsequently published in Nightmare Suspense Library #11:

And, in this instance, the cover art was sourced from an interior panel:

In my earlier post on the recycled Chatto cover I mused rather humorously that Chatto may have been somewhat mischievous in reproducing a previous image. The incidence of recycled cover art on $0.40 cover price Yaffa digests - and, in the case of Nightmare Suspense Library #11 above, resorting to reprinting interior art - has me thinking that something happened in the Yaffa office around this time, related to either licensing, or to hiring of artists, or both. The regular recycling of the contents is not surprising, having been a longstanding strategy by Yaffa, but the recycling of covers has an altogether different whiff about it.

I also note that the stories in Nightmare Suspense Library #'s 8 and 9 are secret service/spy stories, not supernatural/horror stories as both the series title and cover images suggest. Again, some loosening of the editorial reins is evident.

My collection of digests from this mid-1970's era is not extensive enough to draw too many firm conclusions but as my collection grows I expect this is something which will become much clearer.