Royal Bank of Scotland and its partners seeking to buy Dutch rival ABN AMRO for 71 billion euros ($96.6 billion) do not know many of the key facts relating to their target, documents showed on Tuesday.

A U.S. regulatory filing by Spain's Santander for the first time showed details of the shareholder agreement it has with RBS and Belgian-Dutch Fortis to buy ABN, which was signed on May 28.

The agreement said the trio acknowledge they do not know many of the key facts relating to the ABN AMRO Group, including the precise identity and ownership of the acquired businesses.

ABN has agreed to an all-share takeover by Britain's Barclays worth about 62 billion euros. The RBS-led group is attempting to gatecrash that deal with a higher offer, but it is conditional on also buying ABN's U.S. arm LaSalle Bank, which is the subject of a dispute.

The consortium will break up ABN, with RBS taking its investment bank, LaSalle and Asian businesses. Santander would get Italian bank Antonveneta and ABN's Brazil business, and Fortis would take the Dutch retail bank.

The consortium has been given access to ABN's books and has said due to the level of regulation of a major bank it is confident there will not be any nasty shocks in its accounts.

The consortium's agreement said that if Britain's Financial Services Authority increases the capital or other funding requirement of RBS as part of the acquisition then the other consortium members could allocate extra capital to their acquired businesses.

The document shows ABN's private equity business and its interests in Italy's Capitalia, Pakistan's Prime Bank and Saudi Hollandi bank were assets that will not immediately be taken by the consortium members.

The consortium will promptly identify those businesses which will be sold, the document said.

The agreement said RBS and Fortis also acknowledged they could not accurately identify the clients to be allocated to RBS as part of its planned acquisition of ABN's Dutch wholesale clients. Fortis is due to acquire ABN Netherlands business.

In the event the split of clients changes an appropriate value adjustment will be made, the agreement said.

It said in relation to ABN's Amsterdam dealing room, a split of the infrastructure shall be agreed between Fortis and RBS in order to allow Fortis to continue servicing its clients.