In my case a walk in helped with a quicker approval, but it has not
Always been the case.
If you get denied a walk in just be sure to go on your appointment date.
Yes they accept matriculas for ID, mine was expired and it didn't affect it either.
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App sent: 4-4-13
App received: 4-8-13 Chicago routed to Texas Service Center
Bio letter: 4-12-13 Bio scheduled: 5-3-13 (walk-in) 4-17-13
Approved: 5-10-13. EAD mailed: 5-14-13
EAD received: 5-17-13. SS#: App. 5-20-13 Rec. 6-17-13. ID/DL 6/18/13