Please don’t go on about all your other clients in meetings. Smaller clients will only wonder if they will be prioritized and larger clients will be bored. You can mention your other clients in passing at the beginning of the relationship and leave it at that.
Doing cool stuff for other clients might strengthen your case, but let the client find out what you did for them yourself. And let them bring it up, if so. If they find out how strong you’re performing by themselves, or via their trusted peers, the effect will be much stronger anyway.
When you pitch for a new client, have a clear section where you present case studies on what you’ve done for others. Make it clear that you’re permitted to disclose the specific details of these cases. Bragging about accomplishments that are not yours to brag about will only come around and bite you in the ass eventually. And do have a clear start and finish. Show integrity on this, and your client will understand how you will be treating your relationship in front of others.
Be assured that most clients know that you work with other clients besides them. Or, they don’t really care. In either case, they just want your attention, your priority, and your results - if possible a little more of it all than they bargained for in the first place.
It’s like any relationship, really. You have that moment in time when you go through past girlfriends and boyfriends at a level of detail that you’re both comfortable with - and then you move on. When you’re past it, you don’t say “we did this and this together, why don’t we try that, too?” - simply because it’s tacky.
Especially if you’re managing several relationships simultaneously.