In an ITN, is that allowed to include more than the maximum of 540 person months if the additional researchers are financed by another source, but participate in the ITN activities?

540 person months is the upper limit for EU funding in MSCA-ITN and which may not be exceeded for ETN, EJD and EID proposals with a minimum of 3 beneficiaries, while 180 person months is the upper limit for EID proposals with two beneficiaries. If the proposal part B describes person months in excess of these upper limits, this should be indicated separately and be accompanied by a clear explanation of the use of own resources. Under no circumstances should the person months funded by own resources be indicated in the proposal part A (this would create confusion for the evaluators and at the very least result in an incorrect EU budget calculation, etc).
If a partner (non-beneficiary) finance the additional researchers this should be stated in the letter of commitment.