Their site seems amazing; there you can, according to their home page:
Restore your damaged or incomplete vintage sewing patterns from the spare bits and pieces others have donated. Search our inventory of incomplete sewing patterns for the pieces you need. Replacement pieces are free; eligiblity restrictions apply.
Preserve a vintage sewing pattern and build Pattern Points by providing scans or copies of small pattern pieces, or by lending your pattern to duplicate larger pieces.
Recycle unwanted patterns that are not particularly collectible. Browse through the donations and pick out a few to add to your pattern stash — or send us the ones you no longer want but can't bear to throw away. Recycled patterns are free; quantity limits apply.
Trade collectible vintage patterns that you don't want for one that you'll treasure. Wander through the special collection of vintage patterns and embroidery transfers in need of a new home. Collectible patterns require a trade of Pattern Points you've earned.
Post a pattern request so we can help you find that elusive sewing or embroidery pattern you've been looking for, or for a pattern piece or two to patch up your incomplete pattern. Check the posts and see if you can help. Free service; moderated.
Have any of y'all used this service or sent patterns (I have dozens I could probably send and never, ever miss)? If not, what do you do with patterns that are missing pieces? (I swear at mine, it doesn't help to get the dress made but it does make me feel better.)
I should probably get them hooked up with the Vintage Sewing Patterns wiki, no?