300 dpi/ppi standard and resampling

I was just asked to take over a coffee-table book design project for a client in Guatemala. The original designer sent me the packaged inDesign file a couple days ago, and I find that of the 170+ images (photographs) in the book, the vast majority have effective ppi at significantly less than 300. Most are in the 200 – 285 effective ppi range, but many are less than 200 effective ppi and a few are 91.

In my years doing book design, including a couple dozen coffee-table books for artists and photographers, I have stuck to the standard of 300 effective ppi on all images placed in an inDesign file. In the rare case when I haven’t had access to an original image that could meet that standard, I’ve used the PhotoShop Preserve Details resample function to boost an image to 300 effective ppi. However, I’ve never dared to do that with an image that was less than 290 effective ppi to start with, assuming a large boost would make the image look altered.

I brought up the resolution issue with the client in question and she’s confident that her printer in Guatemala will not require that the images in her book be 300 dpi (I’ve worked with this printing house before and yes, they do request on their spec sheet that images be 300 dpi, though I don’t know if they require it).

Bottom line to me is: if the resulting proofs look good to the client, so what if they’re not 300 dpi. It’s her book and her call.

But this experience makes me wonder how rock-solid that 300 dpi/ppi standard is and if I’ve been enforcing it with my clients too strictly all these years.

My questions:

*Is 300 effective ppi still the best? Has that standard changed while I’ve been buried in my work? Is there leeway in that?

*Am I being too cautious with my use of the PhotoShop Preserve Details function? Can I use it for images that need more of a boost – say, taking an image from 200 dpi to 300?

*And this is a wild card question: This client has included on her copyright page the statement “No AI has been used in the creation of this book.” (I imagine statements like these will become increasingly common.) But if I use the PhotoShop Preserve Details function on an image, isn’t that a form of AI?