Hi claire, and welcome.
That's an interesting question. Technically it's the publisher's problem, but none the less, I think it is worth exploring the isssue.
I would start by saying that if the book was conventionally published in book format 30 years ago, then the limitation period of six years in which to bring a claim is well and truly passed. However that applies to the original edition. Publishing a new edition might arguably re-start the clock. You use the word 'images' in the plural; are they photographs or artwork and do they have more than one author? I ask this because if there are only one or two authors involved, then it might be safer to ask for permission for the next edition. The distinction between photographs and artworks may be relevant when I come on to discuss the quotation exception. I assume that the original credits would enable you to track down the author(s) or their representatives.
The next thing to consider is the context in which the images were used. The fair dealing exceptions to copyright found in
section 30 of the Copyright Designs and Patents Act 1988 allow some limited use of images without getting permission, for the purpose of criticism or review of
a copyright work (not necessarily the image itself). The slightly odd phrase "of that or another work" within section 30, subsection (1) is there to cover a situation where the image required for the scholarly work is one created by a third party, and not one created by the subject of the criticism or review. For example, in order to discuss the architectural work of Le Corbusier it might be necessary to examine an image of one of his buildings. However since he did not photograph his buildings, it would be necessary to look for a photograph taken by a photographer whose creative work was not itself being subjected to criticism or appraisal. A similar situation might arise, say, with a painting by Lucian Freud, which required a photograph by a third party to illustrate the critical point being made.
A further element to section 30 is to be found in subsection (1ZA). This was only introduced 10 years ago and several academics have suggested that it might be possible to apply it to images as well as text, although this has not been tested in court. So extending the concept of quoting an image is at least arguable, and might apply to the use in the book which you are updating. That broadens the context away from the narrower one of just criticism or review. And if either (or both) of these fair dealing exceptions might apply, then, due to the manner in which the images have been credited in the book, the formal requirements will have been met, provided that the images are genuinely being used to illustrate or add value to some topic or subject matter which is directly germane to the scholarly book.
And finally I think it is worth mentioning, although it lacks any legal undepining, the convention within academic publishing which tends to be fairly generous when it comes to quoting of written sources (providing they are cited of course). This is tolerated, in the main, because being cited in the work of other scholars is a form of currency within academia, and within the sciences at least, assists in getting grants. This may well account for why no complaints have been raised about the use of the images in the earlier editions.
I'm sorry that this is all a bit vague and speculative. So much will depend on the subject matter of the book: is it a critical appraisal / polemic - in which case section 30(1) is more likely to be of assistance, and also the nature of the images and if their authors might best be described as professional photographers/artists who make their living by selling licences to use their work. Realistically, professional photographers/artists are more likely to want to be paid for the use of their work, and arguably it would be right do so rather than rely on the fair dealing exceptions to deprive them of fair remuneration, however good the case is for invoking the exceptions.