Some progress I have managed to link the new tab to the existing dataset by using "Replace Dataset". However if I now refresh the dataset in one of the older tabs the data in the new tab doesn't update. I have to explicitly click "refresh" on that one as well.

Hi Constantinos 

Thanks for posting in the Lucidchart Community! When importing an org chart and selecting the option to split by page the page tabs generated are interconnected as they were created from the same data import event. That's why making changes to the dataset and refreshing it on one of the page tabs reflects on the others created upon that import event. 

However if the changes made to the dataset involves the creation of a new filter and therefore of a new page tab refreshing the dataset will not cause a new page tab to be created with a different filter applied. This behavior is due to the fact that the split by page is a one-time event – it was designed to occur at the time of the org chart generation only. 

As a workaround you can manually create a new page tab for the new filter and upload the dataset (the same one from which you imported the first org charts by splitting by page) to that page tab. However the org chart generated will be independent from the others meaning that refreshing the dataset on one of the page tabs created upon the first import won't refresh the org chart on the page tab created manually. This happens because although the org charts on those page tabs (the "old ones" and the new one) are connected to the same dataset they were created from different import events. Therefore you will need to manually refresh the dataset on that new page tab (the one created manually) every time you make a change to that dataset. 

Hope this helps clarify things! For more information please read through our Org Charts article from the Lucidchart Help Center. Thanks!