Long overdue post Wedding orders
Firstly, I would have made it very clear, in the initial contract, that the "big book" would be available to purchase at a specific price for a limited period. After which, the price may be subject to increase to reflect inflation in materials and production costs, over time.
Late returning customers who have not be made aware of likely costs increases, in any existing contracts, will have to be reasoned with, perhaps with some kind of percentage discount offered to maintain goodwill. Such a discount could be in material rather than monetary form. For example, you could offer a free portrait and small print, using this as the jump point for, say, potential sale of a larger print or copies. It might seem a sideways step, but it's an opportunity to flatter, and secure other business.
It ought to be reasonable to assume that customers with very overdue orders would realise that inevitable inflationary pressures will bring increased costs. But people don't seem subject to reason when told that they will have to pay more, for anything.