The GURPS TLs were rescaled for 4th Edition. In 4E, GTL11 = ~TTL14-16. In fact, GTL12 in 4E is as high as the TL Scale goes, and is ultratech "magic" - Traveller's Ancients and/or the Galaxiad would fall under GTL12 in 4E.
Your comparisons are a bit different. GT:IW in itself make no references to the Ultra-Tech books or higher Traveller tech much.
GT:IW specifically uses the the GURPS 4 scale found in the 4E Campaigns Book pg. 511, as noted in GT:IW pg. 159. No mods from Ultra-Tech are referenced anywhere in the GT:IW book:
From Campaigns p. 511
TL0 – Stone Age (Prehistory and later). Counting; oral tradition.
TL1 – Bronze Age (3500 B.C.+). Arithmetic; writing.
TL2 – Iron Age (1200 B.C.+). Geometry; scrolls.
TL3 – Medieval (600 A.D.+). Algebra; books.
TL4 – Age of Sail (1450+). Calculus; movable type.
TL5 – Industrial Revolution (1730+). Mechanical calculators; telegraph.
TL6 – Mechanized Age (1880+). Electrical calculators; telephone and radio.
TL7 – Nuclear Age (1940+). Mainframe computers; television.
TL8 – Digital Age (1980+). Personal computers; global networks.
TL9 – Microtech Age (2025+?). Artificial intelligence; real-time virtuality.
TL10 – Robotic Age (2070+?). Nanotechnology or other advances start to blur distinctions between technologies . . .
TL11 – Age of Exotic Matter.
TL12 – Whatever the GM likes!
The technological assumptions are GURPS. The thing to keep in mind, you are shoehorning Traveller to conform to GURPS, so YMMV.
Once the items from IW and the basic books are factored in, the chart changes to
TL0 – Stone Age (Prehistory and later). Counting; oral tradition.
TL1 – Bronze Age (3500 B.C.+). Arithmetic; writing.
TL2 – Iron Age (1200 B.C.+). Geometry; scrolls.
TL3 – Medieval (600 A.D.+). Algebra; books.
TL4 – Age of Sail (1450+). Calculus; movable type.
TL5 – Industrial Revolution (1730+). Mechanical calculators; telegraph.
TL6 – Mechanized Age (1880+). Electrical calculators; telephone and radio.
TL7 – Nuclear Age (1940+). Mainframe computers; television.
TL8 – Digital Age (1980+). Personal computers; global networks.
TL9 – (2025-2127) Pre-Jump Colonization to 2nd ISW. Jump 1; Lasers (Beam and Pulse), Heavy Particle Guns
TL10 – (2128-2235) 2nd ISW-8th ISW. Max Vilani TL. Jump 2; Light Particle and Spinal Particle, Plasma Guns; Repulsors
TL11 – (2236+?) 8th ISW+. Jump 3; Spinal Meson Cannon, Fusion Guns
TL12 – Whatever the GM likes! (?? Jump 4, Jump 5, Jump 6, Dampers and Screens)
History ends in 2303. Hiroshi Estigarribia is given a bio, but his becoming emperor is hinted ("beyond the scope of this book")
The exact years for TL 9-11 for Terrans is from GT:IW p. 130 World Generation. The max TL a world may have depends on the year you generated the world for. The Max for Vilani worlds is always 10.
There are no references to Jump 4, 5, or 6, dampers or screens, so TL 12. Repulsors to deflect missiles exist
And on a humorous note Vilani TL is 10, except for Medical Knowledge which is stuck at TL 7 (GT:IW 160).