AutoIncrement field not populating

I have a custom module, built in Module builder, that has a contract_number autoincrement field.

  'contract_number' =>
  array (
    'type'=>'int',
    'required' => true,
    'name' => 'contract_number',
    'vname' => 'LBL_CONTRACT_NUMBER',
    'readonly' => true,
    'len' => '11',
    'required' => true,
    'auto_increment' => true,
    'unified_search' => true,
    'full_text_search' =>
    array (
      'boost' => '3',
      'enabled' => true,
    ),
    'comment' => 'Visual unique identifier',
    'duplicate_merge' => 'disabled',
    'disable_num_format' => '1',
    'duplicate_on_record_copy' => 'no',
    'audited' => false,
    'massupdate' => false,
    'merge_filter' => 'disabled',
    'calculated' => false,
    'enable_range_search' => false,
    'min' => false,
    'max' => false,
  ),

I disabled auto_increment it to upload some old records from another system for which I needed to preserve the contract_number.

During the upload (a script that generated and saved beans) I also commented out the auto_increment=>true from the metadata file above.

When I tried re-enabling the auto increment I set the auto_increment=>true and in studio set the autoincrement next value at 10000

I also attempted to reset the auto_increment on the table:

alter table wcont_wolframcontracts modify column contract_number int(255) auto_increment

alter table wcont_wolframcontracts AUTO_INCREMENT = 10000;

but got an error at the db level:

Error Code: 1062. Duplicate entry '7260' for key 'contract_number'

But that is the max contract_number in the table and I'm starting again from 10000

select max(contract_number) from wcont_wolframcontracts returns 7260

The result is that the field is not populating at all for new records.

So am I going about this all wrong? What is the appropriate way to define an auto_increment field and ask it to override the auto_increment when creating records from scripts for the initial upload of old records?

thanks,
Francesca