Hi Sadie,
yes your BSC will have a limitation on the number of cells and TRU/TRX you can define for that BSC which ever is reached first .
It is the Hardware Limitation of your BSC. These kind of information you can get by checking which is the utilised elements in the Data File information in your BSC.
In ERICSSON system you can see the number of cell used and defined by SAAEP for sae 298. Similarly there exists SAE for other elements