Applied (for someone else) tried matching to 50k and got this response :
Thank you for contacting Chase about your United Mileage
Plus Explorer credit card account.
At this time, I would ask that you please provide the
offer code as listed on the solicitation received and the
unique Invitation Number included on the direct mail offer
you received for 50,000 enrollment miles. Once we receive
this information, we will be happy to review your account
details to determine whether a rewards adjustment should
be made.
If you were not the recipient of the mailing, we will not
be able to process your request for additional points.
The Chase Explorer credit card application offering 50,000
enrollment miles is non-transferrable. The Offer Code and
Invitation Number included in the mailing can only be
applied to an account belonging to the recipient of the
offer. We are sincerely sorry for any confusion and
appreciate your loyalty as a customer.
If you have any further questions, please reply using the
Secure Message Center.
Thank you,
Margaret Hugh
E-mail Customer Service Advisor
1-800-436-7927