I checked the Encyclopedia thread and only one Levi's link didn't give a 404 error, so here goes nothing. I should add that a lot of the center patch jeans actually aren't vintage (at least the ones I'm looking for) and date back to around 2006. I've talked with Levi's support a handful of times and got nothing out of it. I'm trying to figure out what all the center patch pairs are. I know I haven't quite figured them all out, but I've found a few, though they seem very hard to come by, and obviously aren't currently in production. I'd really like to find a pair with the white "Quality Never Goes Out of Style" center patch. Something tells me I don't have the ideal wording, and if I knew exactly what to type, I could probably find a plethora of those jeans. When I google 519's, I have to block the words extreme or skinny (add a - in front of whatever word you don't want to see in the results) or I get mostly brand new pairs of 519's. Here's what I know so far:
This pair, which can be seen clearly in the first photo and on this store page (which has other photos of the same pair) appears to be 519 slim fit. However, they don't seem to be the normal 519 slim fit. One site I looked at called them "519 slim fit side adjusters". I have looked extensively over the past couple of weeks and was lucky to find that clear photo, as well as that store listing and one Ebay listing which sold a while back. On a side note, I found that 511 skinny leg (or a version, rather) seems to look the same, with the centered white patch and waist adjusters, but they too are hard to find. The 511's and 519's have a white patch that says, "Quality Never Goes Out of Style". There may be others as well.
You may recognize these from the Moonbathing ads. They are part of the "Two Horse Brand" collection, which have a yellow and white patch and say "Two Horse Brand" on the patch. 506 and 511 look identical, while 509 has the addition of a cinch back. There might be other fit numbers I'm missing.
http://josephbennett.co.uk/20790/0x500/thumb10.jpg - Moonbathing ad
https://www.ebay.com/itm/362327161621 - 511 Slim Fit
https://www.ebay.com/itm/EX-CON-Merns-Designer-LEVIS-506-Standard-30x34-Dark-Indigo-100-Cotton-Jeans/362281900617?hash=item5459af1a49%3Ag%3A~EEAAOSw-btavA5H&_sacat=0&_nkw=levi's+506+standard&_from=R40&rt=nc&LH_TitleDesc=0 - 506 Standard
https://www.ebay.com/itm/LEVIS-506-Standard-Straight-Blue-men-Jeans-Size-30-32/263825162810?hash=item3d6d34823a%3Ag%3AsU4AAOSwBdhbULZT&_sacat=0&_nkw=levi's+506+standard&_from=R40&rt=nc&LH_TitleDesc=0 - Alternate 506 Standard?
https://www.ebay.com/itm/Mens-Levis-509-Comfort-Fit-Jeans-W30-L31-Blue-Size-30R-Levi-Strauss-Cinchback/192336081751?hash=item2cc81fb357%3Ag%3AgJMAAOSw~vpZ5cU8&_sacat=0&_nkw=levi's+509+comfort+fit&_from=R40&rt=nc&_trksid=m570.l1313 - 509 Comfort Fit
https://www.ebay.com/itm/LEVIS-503-JEANS-MENS-LOOSE-STRAIGHT-LEG-W30-L32-DARK-BLUE-STRAUSS-LEVH497/282580824984?hash=item41cb213398%3Ag%3Aj9UAAOSwF09ZcbcQ&_sacat=0&_nkw=levi's+503+loose&_from=R40&rt=nc&_trksid=m570.l1313 - 503 Loose I found
https://www.ebay.com/itm/VINTAGE-MENS-LEVI-STRAUSS-TWO-HORSE-BRAND-CLASSIC-STYLE-FIT-JEANS-SIZE-32-34/273314607508?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649 Not sure what this pair is, but it has a sort of curved yoke instead of a straight one, and the arcuates are slanted.
Levi's Engineered has some center patch jeans as well, though I'm really trying to find more of the white patch pairs.