Howdy, Nancy! My advice, FWIW, is that you hand them the SPM and cheerfully ask while the customer is listening if they will handle all IT issues caused by an unsupported platform for free? Ask them if they even had the current SPM? Then ask the customer if they feel confident about an IT company that can't be bothered to check for software compatibility? I've had this conversation many times over the years, and there are way too many IT outfits that make claims like this.
Whatever you do, do not allow yourself to be sucked into their mistake. Trying to make it work after they started this way is a major money pit. A few hours of the IT outfit's time to downgrade the server to a supported version is minor, and you are not included in the customer's wrath because there were problems with an unsupported platform.
A suggestion in the future: When an IT company makes the claim that they've installed Sage products before, ask for a list of those clients as references so you or your client can check their claims. The building industry does this, and it is very helpful, as well as stopping IT salespeople cold when you ask for customer references.