That GFL was a blank designation that meant Graphite Fly Rod and all blanks were GFL perhaps even unto today.
The RP (gen II Graphite) was the first "model," in the Sage Rods circa 1980 or soon after followed in or around 83 or soon after by the RPL or (Gen III Graphite) The LLs came along in or around 85 with the RPLX following in 86 and both were Gen III Graphite. Some time following these or perhaps the same year the RPL+ came out and then in 1994 the SP series hit the market followed by the SP+ in about a year. These were the highest modulous rods yet and built with Gen IV graphite and a new material called Durascrim.
In 97 they dropped back to Gen III I believe and the VPS, the SPL and the RPLXi came out and then in 99 the XP. In 2002 the SLT and TCR, and 2004 Xi2 were the first rods using G5 Gen5 Graphite technology. 2005 brough the TXL, Launch and the the Fli rods all G5 rods. 2006 brought the VT2 replacing the VPS not mentioned above but which came out in the late 90s.
2007 Z Axis. 2008 Bass Series and the ZXL. 2009 the TCX.
Whew too many years have passed since I first sold Sage!!!
On a side note the Gen IV super fast modulus graphite was the highest modulous rod since Fenwick intro'd the Iron Feather and as best I recall both were a Don Green design as he'd come to Sage in 79/80 from Fenwick/Grizzly.