AFAIK, Only with like Mavic, extruded aluminum manufacturing techniques
did sew up rims offer the double concave surface offered there
with a second concave for tire sewing seam..
older tubular rims always had just the one concave surface,
they re shaped an aluminum tube , then rolled it into a hoop.
The experience has just begun..
you got a prep layer of glue, on tire and rim, to allow to cure,
maybe a second layer on the rim, to apply and let cure,
then a layer on tire and rim to get tacky and mount the tires,
then leave them to cure for a couple days , to go..