Virtually all near-luxury to luxury manufacturers do exactly this.
For these two Tesla models in particular, the headlights and trunk line are key differences between the 3 and S, and are clearly identified by enthusiasts. But the majority of the design is part of the brand's consistent motif, making them look very similar to laypeople.
To laypeople, the BMW 3 looks nearly identical to the 5; the A3 looks nearly identical to the A6; the C-class looks nearly identical to the E-class; the ATS looks nearly identical to the CTS; the XE looks nearly identical to the XF; and so on.
For these two Tesla models in particular, the headlights and trunk line are key differences between the 3 and S, and are clearly identified by enthusiasts. But the majority of the design is part of the brand's consistent motif, making them look very similar to laypeople.
To laypeople, the BMW 3 looks nearly identical to the 5; the A3 looks nearly identical to the A6; the C-class looks nearly identical to the E-class; the ATS looks nearly identical to the CTS; the XE looks nearly identical to the XF; and so on.