I recently found a (dead) Osram 13w PL lamp, check my gallery for the pic, and was surprised to find it to be made in the USA. Was this before Sylvania took over?

Yep, during the 80s and early 90s Osram was active in the USA as a specialty lamp manufacturer. They opened a factory in Maybrook, NY making PLs and CFLs. They also made halogen PARs in the USA and imported some types of lamps from Germany. In 1993 they bought North America's Sylvania from GTE, so the Osram brand is less present on lamps here now.

You can still buy some Osram specialty lamps such as overhead projector halogen lamps (ENX and EYB come to mind) here in Canada. Other than that, it is almost always Sylvania.

In the early 90s, one of the local electrical suppliers had even given me a (1991 I think) Osram lamp catalog.

I found some Osram CFLs at a ReStore not long ago.They were made in 1990.