Yes, there is a 6000 limit for event-bundles.
That means that, at this time, you cannot have more than 600 offers per event-bundle.
Please note that each time you create an event with multiple offers, the offers that will be automatically created will be up to 60. You have then the option to add more offers, if you want to, with a maximum number of 600 offers in total.
But what happens if this limit has been reached for one of your events?
Alternative Solution #1:
You can archive the offers that were completed! Archiving will reduce the bundle count and hence, you will be able to add extra offers to your event.
As an example, if you have reached the limit of 600 event offers and then archive 50 event offers, you will then be able to add 50 more offers to the event.
Alternative Solution #2:
Create a Stand-alone/Course connected event bundle every year/ every two years/ etc.
As an example, if the offers of your event per year are up to 120, you could create a 5-year Stand-alone/Course connected event.