the clement sewup repair kits we used had latex patches in them and some 'special sauce' which smelled, worked and felt just like regular vulcanizing rubber cement. The key was to get the tube and patch squeeky clean with rubbing alcohol before applying the 'sauce'. I never had a patch fail on a sewup repair - was much harder to get the tire sewn properly so it wasn't all lumpy/bumpy. That took some practice on multiple cheaper cottons with buytyl tubes before I got the technique down.
Clement Crit Setas & Seta Extras and a number of other high end tubulars all used latex tubes. Wonderful tires/ride, but really tender and not anyhting but pure race rubber.
Other thing I found with latex sewups is that the latex tube breaks down faster than butyl (at least at pressure) so if one got much into a second season with one, that was unusual. If you raced alot you got your money's worth.
The Crit seta extras were superlight and had only a thin varnish of covering over the silk casing. Not a 'wet' tire, they would literally come apart in one race of wet weather riding... like assplode...