"Hi <so and so>, we talked about this matter last in <this email chain or that meeting>, I'm attaching the last <email/meeting summary>. If there's a need to readdress this <situation/decision>, please feel free to let me know and we can setup a meeting to further discuss."
That establishes what you consider to be the facts, based on whatever evidence you are attaching, and doesn't necessarily place you at odds with the client. You always need to figure out how to balance your client relationship with your project needs. Sometimes you may need to give a bit on the project needs to keep the client content but that is surprisingly less than most consultants think.
I've had several clients come back to me after an engagement has completed and mention that they were being intentionally difficult to see what else they could get but documentation helped prevent too much excess on my part. I've even been in the situation where I have acted as the client when dealing with vendor implementation teams and told specifically to be difficult to see what else we could get.
To reflect back what I'm seeing in your language use - to see if I've gotten the gist of it - your subtext / authoring attitude is "ah, you just forgot, let me simply re-inform" but you also don't bother mentioning any particular reason.
Also, do the dev teams listen to the feedback that you provide to them regarding the features that would be helpful / useful according to the client's suggestions?
I employ a team of implementation specialists at a B2B SaaS company. We heavily rely on that team to help guide future product development. But you’ll likely need to be able to translate the ask from 1 customer to something applicable to many customers for the product team to really listen.
One other tip for you- our culture is one of transparency with customers. We encourage our implementation team to be on the lookout for “deal breakers”. It’s best to identify those early and get them a refund than to waste weeks/months only to find that one show stopper right before going live.
You’d think that would be the sales team’s job. I did too, until I hired sales people ;).
Sales people can greatly mis-state product capabilities so be on the lookout for where they let themselves get carried away with selling a solution. I've even worked with them before and gotten called down for correcting their "misunderstandings" in front of the potential customer.
Sales people live for the sale, you should be living to deliver the final solution to a happy/content client.