It’s been debated before but my opinion is that there was never a scripted lever for the right hand. I’ve never seen an original one. They work on either side, of course, but obviously the script would be facing inward if mounted on the right.
The catalog images would have you believe otherwise. My assumption is simply advertising. All catalogs display the bike from its drive side so in order to showcase the lever feature, it was illustrated with it mounted on the right.
The earlier non scripted cast skinny lever, circa 40-51, did not pose this issue. If anyone has a parts catalog showing two separate scripted levers, one left and one right, please offer that up here.