[Wings of Fire]

Nemesis isn't an upgraded T-103.

Oh yes it fucking is. It's a T-103 with a Nemesis Parasite added.

Much later, in 1998, the Arklay facility suffered a viral outbreak in which the entire research staff (bar Wesker) were killed or infected by the t-Virus. An investigation of the facility's mansion façade by the Raccoon City Police Department's Special Tactics And Rescue Service led to their discovery of the T-002, a fully-developed and combat-ready Tyrant. While it was killed by the S.T.A.R.S. officers, Umbrella got their hands on the combat data required to ascertain its effectiveness.

Shortly afterwards, Umbrella Europe began to partner at least Nemesis parasites with the newly-created T-103 series, which were designed based on the same acquired data. The outcome of this development was Nemesis-T Type.