The B List
Because many reception facilities and caterers will demand a minimum number of guests (or charge you for uneaten meals), and because many brides love big weddings with lots and lots of onlookers, guest lists sometimes grow like mushrooms — to the point where the bride (or the MOB) is able to make an A list and a B list. The A list contains the names of the people the bride really wants at her reception — and the B list is filled with the names of guests who will do if her favorite folks can't make it. Is this a safe plan, or a scheme fraught with peril?
Thinking of shifting the invites earlier? You won't be fooling anyone. Most people have also been invited to other weddings at some point, and will wonder why your daughter's invitations are the only ones to demand such an early response.
It's a rude plan, really. Wedding invitations are supposed to be mailed a minimum of six weeks before the wedding, with a requested response time of two weeks prior to the event. These time frames can be shifted only slightly (the invites can go out as early as eight weeks prior, and the responses can be requested three weeks before the wedding). Anyone who has any inkling of wedding invitation etiquette and receives an invitation a month before the event is going to know that they weren't on the original guest list.
In the end, some of your B list invitees are bound to figure out the game, no matter how skilled you are in trying to pull it off. Before you do a tango with two guest lists, prepare yourself for the possible consequences. Let's say, for example, that your irritating cousin Darla calls to ask why she has only just received her invitation to your daughter's wedding, when she knows darn well that your favorite cousin, Marla, received hers several weeks ago. You've been caught. She already knows what is going on, and she's forcing you to either be brutally honest or to fabricate some sort of lie.
Be very careful if you're dealing with an A list and a B list. Your intention (hopefully) is not to insult your relatives; however, because weddings tend to illuminate everyone's true colors (including deep-seated issues of insecurity and the ability to hold grudges), you may suffer the consequences of hurt feelings for years to come. If you can't handle the fallout, it may be best to bite the bullet and invite everyone or to cut the guest list along definitive lines (e.g., first cousins are in, second cousins are out).